You get money from buyer <unless you really trust them> he fills out paper work and in 6 months to a year paperwork is done you hand over suppressor.
Unless the suppressor is on a trust that was made so it could be sold or transferred and then its he pays you amend trust and hand it over this has its own complications and I would consult a lawyer if you dont know how it works.
The same process as buying it from a dealer. Form 4, Form 20s, prints, photos, $200 to the feds, CLEO notification, and waiting. Generally they aren't even worth selling with the financial hit.
one other thing to consider is if its in the same state as you are otherwise its really not worth it 2 tax stamps and a form 3 so almost 2 years wait lol.
Suppressors are a tough sell, as they are readily available and the 6 month wait and honor system cash outlay is tough.
Once an on-line guy wanted to sell me a can and put me on his trust until paperwork came through so I could have immediate possession.
That all sounds good until I considered that if he took me off the trust the next week I'd then be a felon in possession. I thanks but NFW!
Unless it's to a very close friend or family, well....stick to dealers.
I'm looking at buying an m16, a mac10 with can, and another can. This is from a buddy(25 years we've shot together). He's in Dallas, I'm in houston and you did my trust.