Happened to me last week on Montreal's version of Backpages. Alleged provider was a fool of a scam artist---offering two hours of GFE for $120 and demanding electronic payment only before arriving. Person was so stupid they claimed that cash was inconvenient. (This is common in NYC, so I've stopped mongering here.) I was spammed the next day with threatening photos of crushed and decapitated humans and this psycho claimed that I was going to meet the same fate if I didn't pay up for five girls worth of work. I told them to go fuck themselves and blocked the assholes.
Problem solved.
Tomorrow will be my first day ever hobbying in Montreal and no way am I not using a respected escort service.