I wouldn't instantly write it off, but I'm not a buyer at that price. If it's in good condition, and you're comfortable with it after checking it out, make an offer. The worst they can say is no.
Also, when someone says something like an engine or trans has been replaced, that throws red flags to me. I'd want the story, then receipts documenting everything. If anything doesn't line up, I'd run.
Same here. When I see engine or trans replaced and reasonable mileage, I wonder what they did to ruin the old one. I've had well over 100 vehicles and never blew an engine in any of them, regardless of mileage. I've had three transmissions go bad on vehicles I used for mail/newspaper deliveries. ALL three were FORDS.