offer your services on the services section and use escrow if you think the other person could scam you..
for the signature, you get paid later and just check replies to the post to see if the OP is paying and legit

Well.. Instead of 'if you think the other person could scam you..', let's put it another way..
How do you know if someone is trustworthy? Do you, yourself, always use escrow? Or maybe just sometimes? And if not, what are your criteria to decise so?