My first question would be did the shop really remove and replace windows?
if so why without authority?
and if they did so without authority why put a trial version?
More than likely. Because they can and you haven't told them not to !
Its the lazy technicians way of fixing problems. Unfortunately working on computers, a fix can take 10 minutes, or have you pulling your hair out all day. I have noticed BG technicians tend to try the first and then just blast the PC. Many a poor person has lost the lot and then been greeted by the shoulder shrug.
A proper tech, if he has to blat a pc, would take all the data off first, then flatten, then put the info back on. But with the computer monkeys I have met very few will bother.
If its a copy of Win7 they put on there then they aren't trial versions as such, they have a 30 day activation and if you don't activate, it doesn't stop, it just cuts the user down to minimum applications. They also load a clever little patch which tells microsoft what you are using and if it sees its a hooky copy then it deactivates it. As I said, there is a patch to stop this happening but you have to be computer savvy as MS brought out a patch to combat this patch. After all, we wouldn't want to chip away at Microsofts $40Billion turnover.