They cannot be edited, bumped, or replied to by OP once created.
Two auction types would be needed: specific end time or start on Bid and end after X hours (I'd suggest limiting this setting to 1-5 hours) Add a "start/bid" button to these posts that starts the timer for them.
The last three minutes of the post it auto bumps each minute to the top of a separate FT queue then closes.
Auction queue should be sortable by time remaining or number of bids.

Auctions tab next to the FT/ISO/Services would also not be a bad idea.

Agreed, that is what I meant by separate FT queue.

They won’t allow this type because they say people are allowed to sell whatever they want for however much they want and can back out of an auction type trade at any time if they don’t like the price. That being said I doubt this would ever be implemented.

Yeah would require some kind of more committed bidding system than just posting, perhaps an automatic % fine for backing out of a completed auction and a listing fee to limit use.. Probably more work than they are willing to do but it would be nice to have functionality on this site that isn't reminiscent of the early 2000s.