One important thing that I would like to point out is:
DO NOT start working on the job (or at least, do not share the completed work with the buyer in any way) before the buyer has either placed an actual order (through your gig) or has ACCEPTED the custom offer (that you had sent to them).
There have been posts in the forum where some sellers, due to their over-eagerness, ended up sharing the completed work (either in part, or in full) with the client… before s/he actually even got an order… only to have their money robbed from them.
Cuz, then, the buyer can just walk away without having to spend any money on placing an actual order… cuz they already got their completed work (for free!) from the seller.