I ask the owner for a trial/ short term free lease. Long enough for me to get a vet check and to ride him once or twice. If they say no, that's fine. Plenty of other horses for sale.
Occasionally a seller will start hooting and hollering about the risk yadda yadda yadda,,,, yeh what about my risk ? I may end up stuck with an unsound or unsuitable horse. Like I said though, plenty of horses around. They don't like it keep looking.