ebay and buying
Buying/Selling on ebay is a matter of experience. I have bought well over 100+ items without a bad transaction. Things to watch for.
If there is an auction with a very short expiration date,
any ad that requires you to contact seller,
any ad that has email address on it
ads w/cities in the US that don't exist
ads using manufacturers pics and not thier own,
copies of manufactureres ads,
If state of the art technology is on sale >50% below market.
Any item requiring a money order or western union.
Also, read the feedback. The number of good experiences is important, but remember, some people pirate others id's, check and see how many items of the same type and price point they have been involved with.
If someone who has only bought/sold 9-15 dollar items like knitting is selling several $4000 bikes all of a sudden, be careful.
If a deal is too good to be true, it is. Mostly ebay just pulls pricing to about the market or if you are lucky just below it.
I bid on an Orbea Orca once, listed in my city, pics weren't specific. The seller withdrew the listing and said he sold it outright. I believe that the bike was stolen and needed to get out of the city. Somebody in Texas got it for less than I offered. You figure these things out later.