To prevent people from getting scammed, it would be cool to search for usernames in the S/A for free. I guess a lot of people are just too lazy or greedy to search and then get scammed or get sold unperms as perms.

This has been suggested many times before.
It is not needed. If somebody is a scammer they will get tagged as one.

You are innocent until proven guilty.

There are so many people around who have sold unperm items as perm and they're still doing so because it's almost impossible to prove an item has poofed.
It's just to get an idea of who you're trading with, you can still decide on your own whether to trade with that user or not.

No. And this has been shotted down several times as fanta said.