If you are thinking about buying used equipment off of eBay for Video Production, here are some of my tips from recent experiences and mistakes I have made.

First off, video equipment is not cheap, it is an investment that you need to get your value and quality for.   Don't go cheap - in other words, buy quality equipment manufactured by companies with a good reputation for all of your primary gear.   Names like Bogen and Manffrotto are good for tripods and tripod dollies.  They have a good reputation in the prosumer and professional video industry and you can get them on eBay for a fair price if you do the work.

Several things to consider when buying a Tripod off of eBay.

1.) Do your homework.  Find a tripod model or two on eBay and then do a Google search for them to get more information and details and answering these questions: 
A.) How much weight can the head of the tripod tolerate?  
B.) How much weight can the tripod legs tolerate?  
C.) Does it have a quick release so you can easily unmount the camera from the tripod or is the plate built into the head requiring you to unscrew the camera from the head (which can take time). 
D.) Is this tripod made for inside/studio use or is it made for outdoor use and has spikes in the feet?

2.) Ask the right questions, the last thing you want is a tripod with stripped bolts and attachments.
A.) Are there any scratches on it / any dings or dents.   (A small dent in the wrong place could create problems with raising or lowering the tripod.
B.)   Does it come with the quick release plate?  (This question is important, especially if you are bidding on an item entirely by "what you see in the picture" because often times sellers will not show you full detail pictures.  If they don't ask - if they don't want to tell you - then ask for more pictures.)  Generally a quick release plate if you can find it on eBay is not to expensive - about $25.00 or more.   But if your paying for a tripod - it is best to buy one with the quick release plate already attached to the head.
C.) What is the maximum and minimum height that this tripod for sale can reach and still remain stable?  (What good is a ten foot tall extendable tripod if it wobbles when the camera is up in the air?  None)
D.) Are all of the rubber feet on the tripod?

3.) Always ask plainly - Are there any problems or damage to this tripod? (This is a great straight forward question.  By asking them this question - you are making them obligated as though they are offering you a guarantee.  This will help you if there are actually problems they lied about when you actually receive it.   You'll be able to go to Pay Pal, eBay or your credit card company and show proof that the seller indicated that the item had no damage or no more than they indicated and therefore misrepresented the item.

4.) Use a credit card through Pay Pal to pay for the item if it cost $200 or more.   This gives you additional protection beyond Pay Pal's promise to protect you for the $200 to $2000 the seller is supposedly protected for.   Pay Pal also ties up all of the money if you file a dispute and a claim.  My personal example is I bought a G5 Macintosh that arrived much later than promised and guaranteed by the seller and on top of that it was DOA - dying 15 minutes later.  There is then the hassle of shipping back to the seller at your cost - and Pay Pal takes 30 DAYS!!! to give you back your money IF!!! they decide it in your favor.  Right now I have $1,125.00 that has been tied up for a month and a half over a dispute and claim.  That is a long time to not have your money available when your already being screwed by a seller, which brings us to #5.

5.) Don't buy from a seller who has feedback of 98%.   This is a GOLDEN RULE!  The sellers I have had problems with have all had 97.5%.   There are several reasons why not to buy from these sellers.
A.) Once a seller falls below 98% the sales of the seller drop from being protected by Pay Pal from $2,000 to $200.  That means you are screwed if your tripod or other equipment cost more than $200.
B.) A feedback of 97% even for a seller who has 500 or more postive feedbacks - indicates that there are some real problems happening with that seller.   For instance, I made the mistake of buying the aformentioned Mac G5 from a seller who had a 97.5%  At that time I didn't realize how really bad that was.  I had checked all of the negatives left by buyers that he had and I thought they were fair feedbacks that didn't send off any warnings for me.   Well, it was not until after I had the problem and filed a claim with Pay Pal that I decided to go back and check his feedback again.  Once again, I didn't see anything major from the buyers, but.... BUT!!! when I checked the feedback sections of this seller that he had been leaving for people, I saw major, major warning signs in the way he responded and left feedback from people he bought from, as well as the way that he treated those people he sold to.   That particualar seller had a major attitude with his buyers.  It all became very clear at that moment.   So I decided to begin checking the feedback sellers left if they had a 97.5% or less and you know what?   The others sellers had the same kind of attitudes in the messages they left for sellers and buyers.
D.) Every seller I have had a difficult time with pulled all kinds of tricks on me like trying to talking me out of cancelling a dispute or claim by promising to pay me a refund if I closed the dispute or claim.  So I asked Pay Pal's staff and they told me not to do it but to wait until I was 100% satisfied with the results.  Once you file a dispute or claim with Pay Pal - if you close it for any reason - you are screwed if there are additional problems because you can only file one dispute or claim for each item you buy on eBay.

6.) Ask the seller how they will be packing the Tripod for shipping.  Generally, Tripods are solid and sturdy.  But they still need shipped in a quality box with enough padding.   I recently purchased a Tripod Dolly (the wheels a tripod can sit on) and it arrived with two broken solid metal pieces where the Tripod Legs clamp into.  Why? How could this heavy metal break?  Because the shipper used one piece of light bubble wrap to wrap it and one piece of tape on the bubble wrap.  Then he threw in a bunch of newspaper.  Well during shipping, the tape broke, the legs shifted and the newspaper moved around and the metal pieces poked out of the poor quality reused box and snapped off - probably in the truck.   Look for shippers who are going to multi-wrap the tripod in bubble wrap.  Little styrofoam nuggets are not going to help nor will newspaper for a heavy tripod.

7.) Don't rush.   It's eBay after all.  Know how much your willing to spend before you bid or buy-it-now.  Do a search for the tripod your interested in on the eBay seach bar.   Then when the results come up, click the ADVANCED SEARCH button next to the search box.  Now click the little box that says "Completed items" and press GO.   This will give you all the items that match the kind you searched for that sold in the past couple of weeks and show how much they sold for.  This will give you a good idea of the maximum you will want to bid.

Well, I hope these little tips help you as you look for a tripod on eBay.
Of course if you can afford it, it's best to buy the tripod new from a manufactures website or store.  Yes, you will pay more money - but it will be new and have a warranty.  Everytime you buy on eBay, it's like driving in Los Angeles during rush hour.... you just never know when things are going to crash