I think I was a little desperate to pull the trigger, so I could get some new cards in-hand, so I didn't consider one or more of the following:
1.) Feedback - a seller with 1,000 positive feedbacks doesn't mean anything; does the seller have any recent negatives, things that particularly sticks out?
2.) What are the things a seller up for sale - I take a look at a seller's inventory and if see a seller doesn't have much of whatever it is I'm looking for [I maybe looking for a hand collated set for example, but the seller has mostly a bunch of singles listed instead or even non-card stuff], then it maybe a warning sign that they might not have the expertise to have something in-hand, ready to ship.
3.) Item description - the less there is said about something, the more I suspect that a seller might not be able to follow through.
I guess I want a seller to know what he or she is selling and if there is no basic description - it may mean I might not get the exact item.
4.) Buying from a list of trusted sellers - I have to pick up things from sellers that are basically strangers, but it may help to have a list of sellers on eBay that seem to be dependable, whether I'm going to be looking for singles, commons, hand collated sets, unopened boxes or other things.