A post count is a nice indicator.
Something that can be more reliably used for new users who have less than say 200 posts is to check how many posts they have make per day on average. This is located in their profile.
If they insist on having you send by gift, then insist back at them requesting to pay for goods.
I have never had a sale go rotten to date and I practically buy out half the classifieds section. It would be surprising to me if this does not end well.
As one of the people who most prefer to be paid by gift, I would say that one must exercise some judgement in these things.
No sensible person who has run up over 2000 post count, helped various people, relies on people's goodwill for technical assistance and written lots of substantive stuff on the forum would cheat you over $10 of keycaps or $30 of stems. All his 'social investment' would be destroyed.
It isn't even worth it to me to scam 10 people for $250 each. (That's the theoretical max I am capable of since nothing I have is worth more. If after my many and oft repeated rants against overspending on keyboards you still believe I have $800 keyboards to sell just because I can display a photoshopped pix, you will be the fool and not me.)
Does it mean that you can trust me or anybody with similar profile with $100,000 worth of stuff in a huge and expensive group buy? I don't think so. Not unless you've known me personally for a few years at least.
This was the problem in the WhiteFireDragon group buy. That guy got a ton of expensive keyboards and parts from everyone, and somewhere along the line decided that the work versus the temptation was too great and he'd rather give up his reputation and social investment. But he did complete projects for some people, and presumably did not scam the people he had the best relations with, because some of the people who trusted him most got their stuff modded as promised. It was the people who had the least ties with WFD that never got their stuff.
One way is to check out someone's previous posts. If he's got a post count like 20 and they are all super short, you don't have a handle on this person's personality and character. That's not good enough to risk gift payment.
That said, PM me privately this person's name. It doesn't sound like the guy you talked to me about last week.