Sadly, yes, plenty of rip-offs in Vegas. And the quality stuff will not be cheap.
My best advice is to do plenty of research on the Internet before you go and pick the girls that have a good reputation.
If you want just the easy way out, this escort agency
http://www.100proofoflasvegas.com/ has a very good reputation. Decent choice of girls who try to please and they will send the girl to your hotel room. The agency is very customer-oriented and the girls generally get very good reviews for their performance from the punters. The cost is not cheap (USD 400 per hour) but it is comparable to the Macau saunas and in Vegas if you want quality you will have to pay for it.
I would avoid the spa/massage places- highest chance of rip offs or scams, and the quality of the ladies will be very poor, even if they choose to provide anything beyond a standard non-sexual massage. Also avoid the girls who approach you in the casinos themselves. Choose an established escort who has a website, preferably has worked there for a while and has plenty of good reviews, and you will likely do well. Oh, also keep in mind prostitution is offficially illegal in Las Vegas-another reason to use an established escort.