I just don't get why anyone would think it is sneaky to propose conditions to a make an offer.  The facility is there to do exactly that.

An offer to buy is certainly not restricted to price alone, an offer could include terms such as post costs / pick up / combined post / extended payment terms etc

When putting an offer to a seller I often propose conditions, including from time to time making my offer conditional on time of seller response, with a deadline of 24 hours for a response to the offer to hurry up the offer process.