If they try that in Canada the case may be dismissed on grounds of illegal arrest, even if the SP testifies against you that you had sex & paid for it. Compare this case where the guy got off not guilty:
http://www.cannabisculture.com/articles/5161.html
http://www.canada.com/saskatoonstarphoenix/story.html?id=157c77e4-9d4c-47c1-bc41-39000752dbd3
"More is required than proof that the accused is probably guilty. A jury which concludes only that the accused is probably guilty must acquit...."
"The Supreme Court of Canada has since emphasized in R. v. Starr[7] that an effective way to explain the concept is to tell the jury that proof beyond a reasonable doubt "falls much closer to absolute certainty than to proof on a balance of probabilities." It is not enough to believe that the accused is probably guilty, or likely guilty. Proof of probable guilt, or likely guilt, is not proof beyond a reasonable doubt.[8]"
http://en.wikipedia.org/wiki/Reasonable_Doubt
If an SP testifies against you like you say, that alone might not be enough, but if she has your phone call or text message confirming a transaction, you're cooked.
If a jury thinks that there's reasonable doubt*, you're finished, unless an honest and competent judge intercedes. Otherwise, your lawyer might have to appeal.
*There's no checklist. There could be errors in judgement, bad counsel, that might persuade a jury to convict.
P.S. BTW, thanks for the reference source. It's good too, to explain the concept in layman's terms.