Guy inspects a Minor with a view to buying it, looks at the body number...says to himself, THAT'S a bit iffy, & the engine number is WAY out.....upon detecting his doubt, the vendor becomes a bit nervous and short tempered..."got a few more people interested in it...", or "it's bound to have a different engine in it, mate, it's 50 years old", or the classic, & my personal favourite, "it says it's green on the log book...but as you can see, it was originally blue..."
By the time the vendor says "I'm willing to take offers...

...", the prospective buyer has climbed into his car & driven off......
Moral of the story(?)....don't open your wallet until you're 100%....