As some people referenced, companyofmen.org is a great resource. I won't book a masseur unless he's been vetted by guys who regularly post on that site.
Rentmasseur will bias their reviews toward the escort, often deleting negative ones, because masseurs pay the site.... which affects their bias.
But at least you can now e-mail most reviewers on Rentmasseur, to ask for extra details, which can be helpful.. especially if a Google search of rentmasseur + the reviewer's name reveals they've reviewed several other masseurs over time too (i.e., to make sure the reviewer isn't just a random name the masseur himself picked).
But companyofmen.org is my reliable go-to place; they're beholden to no provider, although they won't allow private info to be posted in the public forums or people to harrass anyone.
You can get a sense of whether the provider is cool in the public forums by searching for the masseur's name, and e-mail guys directly privately for all the discretionary details.
Sometimes, there's a guy I really have an itch to see on rentmasseur because something about his picture or description really intrigues me... but if there's no information on companyofmen, and no one on rentmasseur I can reach out to whom I'm comfortable in, I will not book. It's just not worth it, as there are definitely scammers on Rentmasseur.
A friend of mine just saw one such scammer, but had he done his research on companyofmen.org, he would've learned the guy wasn't the one in the pics, did a lousy job, and would try to pressure the client into paying more for extra services. (He's lucky it wasn't worse.)
Also, there are great posts for newbies on companyofmen.org, answering all those "dumb" questions you may be afraid to ask when you're starting out! And nice guys on that site who mentor newbies too sometimes.
One of them mentored me when I started out, and now I'm his prodigy and he's very proud of how far I've cum.... !!
And I've mentored a few newbies myself now too! It's fun to mentor a newbie and help him get the courage to have his first erotic massage when it's a big success and he can't wait for his next!