Since I use both venmo and cash, I typically will tip between 10% to 25% of the session cost and will make my decision depending on how good the massage and overall experience was. And what do you know, it ends up being pretty similar to what WVChris mentioned with either a $20 or $40 tip lol.
For the masseurs that give you a short massage, lasting between 30 to 45 mins and then give you a release, I don't bother tipping them. I would much rather tip the "rockstar" masseurs that give you full 60 or 90 mins you requested plus a release afterward.