I'm with you there. I bought a K a while ago and had Dugosh do a pre-buy turned annual. I didn't stay there all the time, but dropped in a few times during the inspection to check on things etc. They caught some stuff, but the biggest issue at the time I caught on the test flight (AI needed overhauling - had an issue that rendered the AP unreliable).
Last year I bought an Eagle from Jimmy, that was already at KGGG for an engine install. Maxwell did the annual, which in my mind served as a pre-buy. I spent a week in Longview, TX. Dropped in daily - same drill. The Maxwells were very accommodating, answered all my questions, addressed all the issues that were found (things like a blown voltage regulator, worn tires, adjusted the speed breaks etc.), and did a couple of extra things I asked for, like spraying corrosion X in the wings (I was bringing it to SC near the ocean) and other minor stuff. Paul also took me up on a flight as he was breaking in the engine, which doubled as a test flight and I was able to check avionics, AP, rigging etc.
After 70 hours, a few things popped up here and there but I don't think any of it could've been prevented at the time. Just normal stuff that breaks in an airplane.
My rationale for not insisting on an independent pre-buy was simple: between Jimmy and Maxwell, they have built a solid reputation over the years, which I don't think either would want to tarnish by selling you/signing off on a plane riddled with issues, or try to hide anything. If I were buying from an individual or a lesser known/less specialized broker, I'd sure want a pre-buy, as I did with the K. But with the plane already in East Texas, I'd choose convenience and Maxwell's reputation over flying it elsewhere for a pre-buy.
My 2 cents. I'm sure a lot of people here disagree.