I would suggest to talk to the original builder if that is possible.
If you're buying it from the original builder, you can often get a good idea of how much care and attention they put into building it. Another clue is the finish and appearance of the plane. Even a superficial look at a poorly built plane will show signs. Look for things not fitting or operating correctly. Did the builder take the time to decorate the plane nicely? That shows that they took some pride in the project and were prepared to invest some extra time and money on it. The finish says a lot about the builder. By the time a builder reaches the end of the physical construction, there is a strong urge to get it into the air. It may have been built to a very high standard, but if the builder was prepared to take the extra time to make it also look nice, that suggests that they are thorough and patient, two very important attributes of a good builder. I think that how the builder finished the plane suggests how they built the plane.
Also, if you are buying from the original builder, ask to have a look at the build log. If it is almost or completely non-existent then I'd run a mile... in the opposite direction. In contrast, a builder that trots out something the size of a dictionary, with lots of pictures and drawings and explanations, and then bores the sox off you describing how he solved the tricky door latch issue, has probably built a good, safe plane.
Also, if you're buying from the builder, you can ask them whether they varied anything from the original build instructions and if so, why.
Ask about compliance with ADs and SBs on the airframe and engine. Have a look at the maintenance log and other documentation. Look specifically for documentation of builder-initiated mods made after the first registration.
Ask about damage history and look for signs of any repairs made to the plane. If the builder/owner admits there is any damage history, look for it in the logs. Damage is not necessarily a show stopper, but it must be properly repaired and documented. Also it should be factored into the sale price.
Ask other people who might know anything about the plane. Ask at the airport where the plane is based and ask here on the forums.
I'll probably be stoking the hornets nest with this, but did the builder put a new or second hand engine in the plane when they first built it? If they put a second hand engine in, that suggests to me that they were building on a tight budget and there might be other areas where they went for the "cheap" option. Would you buy a car that had a half-life or near-end-of-life engine installed when the car was new? I wouldn't.
All of these things will be checked by a competent L2 or LAME, but a lot of them are things you can check before you start throwing money at professional inspectors.
Finally, if you're buying from the builder and they show any hesitation to be completely honest about any aspect of the build or maintenance of the plane, run a mile in the opposite direction. Your life could depend on it.
EDIT: One last thing, take your time buying a plane and be prepared to walk away if you're not completely comfortable with any aspect of the purchase.