We've stayed in timeshare properties and private residences in Europe and Mexico without experiencing any serious problems. In fact, they've generally exceeded our expectations.
Still, things can go wrong, as one couple discovered when renting a once-in-a-lifetime Paris property without hot water. Even though the travelers rented it through a legitimate agency, even though they paid extra for a "rent with confidence" guarantee, even though they were supported by a well known travel "ombudsman", they were still out of luck.
In the final analysis, you pays your money and you takes your chances.