Unfortunately my recent experiences have hardened me a bit on this subject. I bought a motor from another racer across the country who said it only had one race on it and some break-in time. He guaranteed that it would run and that it was in good running shape. To make a long story only slightly shorter - it didn't run, and when I had my engine builder take it apart there were virtually no usable parts in the motor! I ended up getting one end cast iron, one "N" rotor, and an oil pan and baffle for my money, because the guy who sold it decided to ignore his guarantee. That "cheap" engine has cost me a ton of money and, even worse - half of my racing season and I still don't have a running motor. Sometimes it ends up cheaper to pony up the cash up front for a local trustworthy builder than to scrimp onsomething that is a complete waste of money.
Just my two cents worth - the biggest shame of the whole situation is that up until now I've never come across another racer who wouldn't give the shirt off of his back to help out - it has really shaken my faith in people.