Like everything else in life, You need to do research before you dive into anything. I own several factory made suppressor's- Thunder Beast / Mack Brothers / Silencer Co., and they get top dollar for the suppressor's that they make.
The truth is you can buy one of several high quality Solvent Traps or separate parts kits and build your own suppressor that will work just as good for 1/2 the price.
Plus building one doing a Form 1 instead of buying one doing a Form 4, you will get your tax stamp in less time. The shortest time I ever had with a Form 4 was 4 month's. I just got 3 Form 1's approved in 2 1/2 month's.
The rimfire suppressor that I just built cost me $300 including the price of the tax stamp. I saved over $200 from what I have invested in my Spectre II and tax stamp. The sound suppression is pretty much the same.
If people don't follow the rules when it comes to building suppressor's or any other NFA Class 3 item's, then yes, you risk being arrested and going to jail. I play by the rules, and don't worry about anything that I'm doing as being illegal. If you don't modify anything before you get approved for the tax stamp, you have nothing to worry about.
If I or anyone else that owns or has built anything that requires a tax stamp can learn what the laws are, then you can do the research on your own. It's free information, all on the BATFE website, or you can ask a local Class 3 FFL and they will tell you what you need to do.