I’d say figure out your maximum allowable offer and if it is lower than your seller desires, apologize that your offer is lower than they want, but tell them it is all you can offer. You have to make sure the deal is worth doing, so your max allowable offer bakes that in.
Anyway, leave them a card or something with that offer and ask them to call if they decide that they want to accept it later down the road. The seller may eventually call you and accept the offer.
I think you have to pass up the opportunities that aren’t worth doing. This seller has enough of a profit motive to question their motivation. For now, you should probably move on.
By the way, I have such a situation going on now on a mobile home. Mobile home is sitting vacant and requiring grass to be mowed and lot rent to be paid. All the while the seller is holding out on a cash price. Their holding costs may eventually wear them out and perhaps I’ll get the call.