I consider myself an average baseball card collector, and all I intend to do is offer any help I can from my own experience. This might be useful  to you if you mostly buy and ocassionally sell cards on eBay. You can read eBay's summary of  what card grades mean, so I'm not going to repeat that here.

 Most sellers tend to exagerate, at least a little,  the condition of the cards they offer. It's human nature. I have seen badly miscut cards listed as EX++. But also realize that a card can be of mid-range quality and properly be called Excellent, following the grading standards of the professional card grading services. Don't ever believe somebody who has cards listed and claims to know nothing about them. Nobody who is selling cards is that stupid, but they hope that you are. As far as collectable cards are concerned, eBay has pretty much become like the New York Stock Exchange: For the most part, cards sell for about what they are worth. To get a bargain, you have to do some work, which means checking prices intensively for a significant amount of time.

  One of eBay's most useful tools is the ability to check on recent sales. This can keep you from overpayimg. Click on the left side selections (completed auction/last seven days) and find out what the card you are looking for has sold for recently. Check scans carefully. People who post bad scans are probably hiding some flaw.  Look for fairly priced shipping. Take advantage of combined shipping and buy more than one card from dealers who offer it. All fair-minded sellers should. Obviously, .50 cent common card is no bargain if shipping is $3.50 or more.

  One of my pet peeves is how buyers tend to undervalue graded cards that aren't 8s or above. A graded 5 (EX) by PSA, GAI, SGC or Beckett is a sure bet and in most cases will be better than an ungraded card described as NMT (near mint), in my experience. So if you're looking for a bargain, bid on 5s and 6s that are graded. You're likely to get the card for less than the cost of grading, and then you've got something that won't deteriorate. If you'd rather have a raw card, just remove it from the plastic case, for goodness sake!

 There are hundreds of honest sellers out there. Reward them and give them repeat business. Don't deal with people who look to make money on shipping and who don't grade their cards fairly. You make ebay better for all of us this way. Thanks!