Replying to Boot causing ankle pain/burning

I was planning on buying these boots off a friend so he let me try them out for the day. After about a half hour I felt a burning feeling in both legs/feet but continued on. About an hour after that the pain became much more severe and was very hard for me to continue. After I took them off my ankles were in extreme pain and I couldnt even walk. Was this because the boots were heat molded to his feet or the boot itself. Im getting these for a steal so I really want to figure this out. Will reheatmolding them solve my problem? They're in my size and have a good fit but using them for a decent amount of time has became a problem. Im really hoping that getting them reheatmolded will fix this problem please give me some advice. Thanks