I'd say dealership, the mechanics do not have any tools to make sure the belt has been tightened to the Company specific tension. The mechanics just do it by "experience" and "guess work". I have seen one mechanic trying different belts on a Honda City, the same doing "smoke" caused by incorrect tension on the belt and finally he got it right, at least for the time being.
There is a special tool used for checking whether the belt's tension is correct or not. I have no idea if local Toyota dealership has those or not but at least they will not be doing anything by "guess work".