If it sounds too good to be true, it probably is. While I don't know exact numbers for what is standard, because I don't shoot pro porn, I do know that if they're offering multiple thousands of dollars, or tens of thousands - probably a scam. I would also be hesitant of any offer on Twitter, unless it's someone I'm familiar with reaching out and saying "Hey, I'm in your area in two weeks, wanna get together and film?"
Researching them can never hurt. Check out their existing work, their website, their social media presence. Those can tell you a lot about them.