There is a maximum length of time the issuing bank is allowed for making good on the funds. It stems from the federal reserves minimum processing times.
If you remember, in the old days, a check might take 2-3 weeks to clear. Not today. Depending on which reserve district it is drawn on, as little as 1 day to clear. I think the federal reserve allows 5 days max.
Most fraudulant MO's lack obvious things when presented to a bank. Watermarks, indicia, threads, ink type, etc. Most criminals are not sophisticated forgers.
So, in answer to your question, I would say "Ask your bank how they handle things", as you are at their mercy regardless of what you do, after the gun leaves your hands.
On another board, the Litt's debacle, and the difference between British and US laws was recently discussed as applied to stolen firearms. It was good reading.
So, 1. Ask your bank how they would deal with it,
2. Wait an extra day before shipping.
and 3. Set up an account just for such transactions, and keep a long arms length away from your household stuff when doing firearms transactions with unknown parties.
Better safe than sorry.