As for what will happen...
The scammer will send you a check/money order/similar for more than he owes. He will ask you to cash it and send the extra to another party - such as "his groomer" or whatever - and give you an address to mail it to.
Up to a month later the original check will reverse as bad, but by then it will be too late to recoop the money you sent on.
And the scammer will have access to your bank account number from the check you wrote (not that he can really do much with it).
So basically never send money TO a client - at least one that hasn't used you before - and you are fine.
I play along with the scammers to see how many fake checks I can collect
. Now my email address must be blacklisted because I haven't gotten any more in years.