Just sell it with a quitclaim deed or do owner financing with your buyer.

For a decent quality note with a decent yield, there are a multitude of buyers at any point in time.  

Is this the best way to use funds to appeal to more buyers, or leave it as is and offer credit.

How do you qualify a buyer for a 4plex?

Should I at least get it under contract and see how the buyers react to it?

Yes, there are savvy and enlightened buyers who would buy it.

He probably will never be available to show it to your end buyer. 

I haven’t read the last FARBAR version in detail, but in prior versions:  if the buyer doesn’t obtain financing approval by the date set in the contract, usually 30-45 days, then Either party may cancel the contract, in writing.....no automatic loss of EM.

If the lender had trouble get comps they like, the seller will have the same problem with another buyer and will probably understand that it is the property not you that is there problem.

Even if you repair the foundation, you will have to disclose it to the end buyer, which can scare them away or reduce the value.