I disagree about the cheap massage places
I lived in Phnom Penh for several years and became a regular afternoon (between my teaching classes) customer of "SONY" massage parlor (just around the corner from the Heart of Darkness). The girls could be hit or miss but I went there often so I learned which were the true gems.
Two or three of these gems were some of the best I ever had (in my life). Very attractive, fresh, full service, good performers, fun to be with, not whiners, sexy, very young (K11 had just been shut down and they were shipped into town from there), etc.
I was a regular so the mamasan always gave me a one dollar discount (I paid four dollars instead of the usual five). Or she would let me have two girls for seven dollars. And I always gave the girls a dollar tip each (and also occasionally to the mamasan and the guy out front who watches the motorbikes. And sometimes I would take in some fruit or candy.
I took lots of new customers to them, too. So they really loved me there, haha!
One of my favorites there "graduated" to the fish bowl over in the "New York" hotel, on Monivong, where she started dating on of the chefs. She phoned me on 2-3 occasions and wanted me to "break in" a couple of her friends who were new to the business. Of course I was glad to help her out, hehe!
One of the other favorites from SONY ended up as a "kept woman" for an older wealthy Japanese businessman at his ocean view villa just outside of Sihanoukville (she hated it but the money was too good to refuse).
I returned to Phnom Penh recently and visited SONY. All new girls and staff. No one knew me this time. Was told it would be $10 + tip, take it or leave it. I took it, regrettably, and the stunner (mistake! ) I picked was totally useless in all regards. So useless in fact that I couldn't maintain an erection. A very antagonistic encounter, to say the least!
But I had already paid in advance (unlike the old SONY) so I was a very unhappy customer.
So my point is that if you are a regular customer and know the girls/staff, there are some gems to be had at these places. Just use common sense regarding money, jewlery ripoffs, etc. ALWAYS keep your pants with you. In the shower, in the bed, etc. I never had any problems in this regard. And never take anymore than you would care to lose (just in case.)