Agreed with everyone else telling you to skip on the ones you were originally looking at, and it sounds like you may have made that choice already.
Just to throw my 2 cents in, I also use glass tanks like Bogertophis for my BP, spotted python, and two hognoses. For the BP I've had a tremendous amount of success making some very cheap modifications to the enclosure and my set up now holds humidity and heat very well. I know you may not want to, but it is the cheaper option just to modify something you already have.
That being said, I have a Animal Plastics T10 on order for the BP because he's gonna need the room eventually. For what you were looking to spend on those first enclosures you posted about, why not take a look at some of the PVC options available? Animal plastics, while it'll take forever to get them, has some good options and their T8 is currently on sale for just a few bucks more than what you were gonna spend on those used ones.
Also to echo what is being said about used enclosures. You have to consider why that enclosure is empty. Is this person just getting out of the hobby and rehomed the animal that was in it? Or did the animal have something wrong with it that may still be present in there for your BP to pick up. Take your time looking and then be sure to do a thorough cleaning before moving your snake into anything new or used. It's up to you, but for the price of some of the used enclosures you've linked, you might as well get yourself something new.