You are making my point from 180 degrees away. If you are not qualified to make the judgement your friend did, then what? And another thought I wanted to share is documentation. In this environment (as opposed to steam gauges and magnetos), system documentation should be fairly complete and understandable. I am proposing that elegant documentation ( including fault analysis ) and workmanship will significantly enhance marketability or compress the tire kicking phase for knowledgeable buyers.
If you're not qualified to perform the analysis and you don't have a friend that is qualified, I would think hard about purchasing an EAB is the correct decision. Otherwise you are putting quite a bit of blind trust with the original builder, and if applicable, any subsequent owners.
I fully agree about documentation and ensuring it's current. Not just schematics for the electrical system, but data wiring schematics as well. Also, not to over look transponder checks, pitot-static checks, maintenance records, etc.
One of the things that initially caught me off guard as a Technical Counselor, was the amount of calls that I get from folks that have absolutely no clue about how things work in their aircraft.
If you purchase an EAB, you better have the expertise to understand all the systems, or have a close friend, or trusted A&P that does. Otherwise you are taking on some unknown risk. If you don't have the expertise, you need to find a mentor to help you through the process.
In the case of my friend, the 2nd owner rewired the power and didn't document his work. The only information my friend received was that he used a Nuckoll's schematic. Now my friend has to play detective. He purchased the Nuckoll's book and determining if it's a Z-11 and if so, is it wired per the original schematic or are there deviations. He's teaching himself in the process, but he does have access to several SMEs to provide advice.