Purchase questions - used vs new. Heat pump vs Natural Gas

[Watermom]

Hi Clueless and welcome to the forum. I can't answer all your questions, but I can tell you that you will definitely need a new liner. Liners that have been drained are not usually able to be used again as they become brittle over time and cannot usually be stretched back into place very well. Plus, it is already 8 years old, so you will definitely need a new one. The pump and filter are anybody's guess. You can always replace the cartridge. The pump? Maybe just give it a try and see. You'll also have to inspect the steel walls to look for rust. Hopefully someone else will come along here who will better be able to talk heaters with you as that is not something I know too much about.