Picking up where someone left off?

[Joda]

I go back and forth between getting a kit mostly done, to get closer to the flying part faster, or one that's far from completed, so that I know what work has gone into it.

The advice I always give is that, if you really want to fly, and are looking to get the project done so you could fly, maybe you ought to think about buying an already-flying airplane. If you really want to BUILD, and are looking forward to the building process, and the flying is just a bonus, then buy a project. Even a project that's well along still needs a LOT of work, meaning time, and you need to be willing to make that commitment before you dive into the project.

how do you evaluate work in areas that are closed off already?

You can't. This is one reason that very complete records (especially photos) are very valuable. That, and a thorough debriefing of the builder (if possible) to ask questions about how certain things were done. Also, what you CAN see is usually a pretty good indicator of the quality of stuff you CAN'T see. How do you think us DARs do it when we go to look at a ready-to-fly airplane? You have to be able to evaluate based on what you can see and feel. If you don't feel comfortable making that type of determination of build quality, then enlisting the help of a knowledgeable EAA Tech Counselor, experienced builder, or A&P mechanic with the proper background is important.

How can you tell if a person deburred before they pulled the rivet?

You can't. Again, you need to ask these questions when talking to the previous builder(s).

I guess the bigger question i have is how do you evaluate the build quality of the builder.

See my comments above!!