Is there a technique to see what your seam/putty work is going to look like before you begin painting it?
Some of my seams/putty work look/feel great to me but once the paint goes on the seam is very visible!
There are two I know of. Both involve painting the seam, with either a grey primer or silver. Both are great at highlighting any flaws in your work. The drawback to using the silver is that it must either be removed or primed over once you are satisfied with your seamwork and prepared to start laying on your colors.
You kind of answered the question yourself[;)]. The answer is to paint it with a coat of primer before the color coat to see any problems to fix.
A silver sharpie marker works well also , i use this before I prime to help spot problems,
High power magnification, at least 10x, also helps. I have a 18x mineralogist hand lens I use to inspect for the tiniest of flaws.