Hook, line and sinker
Quite frankly, for the $500 cost, you could have brought another cheap laptop or pretty near another one. I would remove it from their grasp and go elsewhere. Of course this is up to you. As the other posters offered, there are s/w virus scanners, etc., and its getting to be alot to swallow if the HD went bad. It went bad under their care and wasn't described as such when you dropped it in. Of course now its too late to verify they are dealing with your system parts, but I tend to lean on the negative side of things. I think there is something at play here, maybe wrong fix or failed diags. All this now open to debate.