Buying good used systems sometimes makes it super easy to develop multitank syndrome...I have a bunch of tanks and they were all used fixer uppers. I wouldnt be in the hobby tonthe levek i am otherwise. If you're patient you can pick up used setups for a song. When we moved and I got back into the hobby, my wife bought me a red sea 130dd for $250. She fell in love with the tank so I bought her a 32g biocube for $130. Then I was running out of room so I picked up another red sea 130dd for $200. Then she wanted a tank just for her mushrooms, so i snagged a 9g full flex for $50. All plug and play systems, i just had to add rock, sand, water and livestock. I've since upgrade some lights and pumps, etc (again all used gear).
That being said, NEVER trust anyone used heater. I run inkbirds on all my tanks and heaters get replaced every year or so.