I've been on here a long time, and done many [i]many[/i] sales and trades with all sorts of people on basschat (and bassworld as was) and never once had an issue.
You'll find the vast majority of people on here are the salt of the earth, although there's always a few characters to avoid, I hasten to add I don't know any on here.
Follow the advice above, try and do some research into the person you're trading with and if they have good feedback etc, then you shouldn't have a problem.
There's always an element of trust when posting stuff, but it's a lot safer on here than on somewhere like ebay because most of us on here know who most of the users are. Just be a little wary of new members who haven't posted very much. You do get the odd member who only comes here to sell stuff, and people like that we don't know much about.