When buying anime and manga merchandise on eBay, you have to be careful to make sure what you're getting is not a bootleg and that you're not overpaying for something that could maybe be easily bought elsewhere for cheaper. Here are a few pointers I think will help buyers:

DON'T BUY...

• Anything in Chinese.
  If it's in Chinese, it's most likely a cheaply manufactured bootleg. This is most applicable when it comes to artbooks. For books, ask the seller for an ISBN if you're not sure. If they don't reply or don't have one, don't bid. I've also noticed that the photos for many bootlegged artbooks are taken at an angle.
  
• Region free DVDs.
  Anything that's region free (region 0) is almost always a bootleg with bad subtitles, or just fansubs burned onto video DVD that you could download for free. Don't buy if the DVD packaging is in Chinese, includes Chinese subtitles, has more than 5 episodes per disc, or is region free. FYI, North American DVDs are region 1 (3-5 episodes per disc) and Japanese DVDs are region 2 (1-3 episodes per disc). You can find a complete list of anime licensed in North America at AnimeOnDVD.com
  
• Anime on data CDs/DVDs.
  For one thing, this is unethical and illegal, but also, you're most likely getting fansubs that are available for free.
  
• Doujinshi on data CDs/DVDs.
  Don't waste your money.
• Cheap soundtrack CDs.
  Japanese CDs are in general pretty expensive. Anything listed for $15 or less (except CD singles which may retail for around 1250 yen, about $12.50) is sure to be a bootleg, unless they are a domestic release. Check for company logos and know the names of known bootleg companies (eg. SM/Son May, Ever Anime, Smile Face, Alion, etc). FYI, Japanese OSTs generally cost $25+.
  

WATCH OUT FOR...

• Posters.
  
  • Posters that are folded or have more than one series on it (ie. a series on one side and another on the back) are most likely extras from magazines such as NewType or Animage. Chances are the seller is asking for $5+ for that one item when you can buy the entire magazine, including the extra(s), for that same price. This also pertains to any other item that contains more than one series on it, such as clear files or calendars.
  • Sometimes the issue that came with these extras are sold out so those are harder to get and may not be bad buys. Just watch out for the extras from current issues because those you can easily get the entire magazine plus extras for the same price or less.
    
  • Laminated posters (usually 21"x15" or something) are NOT official Japanese posters so I suggest you don't waste your money on them.
  • Official Japanese posters are most often B2-sized (728x515mm, or 28.7"x20.3"). Yes, they're big... They also always have copyrights or trademarks printed on them, or have a sticker.
• Wallscrolls.
  Official Japanese wallscrolls are expensive, averaging about $30 each. If what you're getting is not a licensed wallscroll by Great Eastern (GE) or other North American manufacturer, it's most likely a bootleg. Always check for company logos and copyrights/trademarks, which will be printed on all official wallscrolls, whether they're Japanese or North American.
  
• Items with low BIN and high S&H.
  Though it still may be a good deal for buyers, sellers who use this tactic should be avoided in general because they're going against eBay rules. They make their item seem like a good deal but get you in the end with high shipping charges. If you decide to deal with sellers like this, be sure to rate their Shipping Charge accordingly.
• Overpriced Japanese manga.
  A Japanese tankoubon (volume of manga) usually retails for under 600 yen ($6 USD) so I suggest you don't buy manga in which the total (item + shipping) costs more than $15. It's ridiculous to pay $10 per volume, not including shipping. Phone book manga (usually published monthly with many series in one issue) generally retail for $6-8, so don't go paying $15 or more for one issue, plus outrageous shipping.
  
• Bags, T-shirts, watches, and other weird merchandise.
  Items such as these are most often not official and usually cheaply manufactured in China. Official Japanese tote bags and T-shirts usually retail for 2500-3150 yen ($25~$31.50 USD), and a good watch can retail $70 or more.
• Items with no photos or items that use stock photos.
  In this day and age, almost everyone has a digital camera. Heck, even cell phones have cameras so there is almost no excuse for listings without photos of the item. When stock photos are used for DVDs, make sure the DVD is region 1. Many sellers selling bootlegs will use stock photos and default disc descriptions.
  

DO...

• Your research.
  It's always a good idea to check the retail price of the item you want at Japanese online stores to avoid overpaying for items. Amazon Japan is a very good place to start. Some things, such as figures, can even bought for a decent price at reputable American online stores. Make sure you know what types of items are available for that series in order to avoid bootlegs. Also know the approximate weight of items so you don't get ripped off on shipping.
• Check for company/publisher names.
  Any reputable company that's taken their time and money to put something on the market will certainly put their name on it. In the case of Chinese artbooks, make sure the publisher shown on the book (if any) matches the one stated in the item description, if it's mentioned. I've seen books that say they're published by one company but the spine shows the original Japanese publisher.
  
• Check the seller's feedback rating, including DSRs.
  Always know who you're dealing with before you commit to bid/buy.
• Ask the seller questions.
  If you're unsure about anything, ask the seller. If they do not reply then don't bother dealing with them.
  
• Check the item location.
  Be cautious if it's from an Asian country other than Japan. By knowing where the item is being shipped from, it's also possible to get a rough estimate of how much shipping should cost.
• Check search results from eBay Stores.
  Sometimes you can find the same item for cheaper, but they don't stand out as much since they can show up at the bottom of search results depending on your viewing options.
  

REMEMBER...

• Japan is very strict when it comes to copyrights and trademarks. ALL official merchandise WILL have some sort of mark on it, usually the name of the creator, artist, animation studio, and/or TV channel that airs the series. (Sometimes it's just the initials of names or first letter of companies if the item is small, such as a pin or mascot fastener.) Items often have a small sticker with the manufacturer name or animation studio on it, and prices are also often printed with a box around it either on the item itself or on the packaging.
  

eBay is a huge marketplace where you can find good deals, but there are also people who try to trick buyers. In the end, it's your money and you decide what to spend it on as well as how much you are willing to pay, but I think that by keeping these points in mind, you will be able to avoid the bootlegs and make better purchases. Use common sense and don't deal with anyone you think is shady. Don't hesitate to report to eBay sellers or items you feel are in violation of the rules either.

Here are some average retail prices (in USD) for common merchandise:

• Japanese tankoubon (volume of manga): $3-4 for regular series, $6 for BL/yaoi series
• Japanese phone book manga: $6-8
• English-translated manga: $5-15 (usually towards the higher end for BL/yaoi manga)
  
• Artbook: $10-25 (more if they're hardcover)
  
• Shitajiki (pencil board): $2
• Clear file: $3-5
• Laminated card: $1
• Bromide card: $3
  
• R1 DVD: $15-30 each (doesn't include box sets or limited editions)
• R2 DVD $25-60 each (doesn't include limited editions or OVAs, which can cost a lot more)
• Magazine: $6 (NewType, Animage, etc), $8-9 (Megami, B's LOG, etc)
  
• CD: $25 for OST or album, $10-15 for singles
  
• Trading figure (random): $6
• Trading card pack: $4-6
  
• Model kit: $6-10 for 1/144 Gundam, $15-25 for HG 1/100 Gundam
  
• T-shirt: $25-30 ($15 for North American licensed ones)
  
• Notepad: $3-5
• Doujinshi: $2-6 (can vary greatly because there's no standard pricing)
  

Happy buying!