When buying a used tank, do you keep the fish or give them away?

I think it really depends, if the fish is going to fit the tank (which in many cases from someone else isn’t the case), or can go with the theme I was planning, I would keep it. Otherwise I tend to just either try to sell them off or give it to a local store for free if they can take care of it.

This sort of thing is never a welcome surprise, and I try to ask about it in order to avoid it happening. But when it does, I keep them if at all possible. Otherwise, I keep a couple of smaller spare tanks around to accommodate them until I can relocate them.

have done both

This is not a situation I have dealt with, but I would like to think I would keep them, rather than getting rid of them! I can understand why people do take them to pet stores, though, the tank might have had a different setup in mind and now suddenly here are a multitude of fish you hadn't planned for. It can be harsh!

I always keep the alternative tank just in case if I need to make use of it in some of such circumstances. I make sure to avoid used tank with fish in it. I usually get them empty in that case. I hope that in near future I may have to work with tanks which require less maintenance as well.

It really does depend for me, if the fish fit in the tank and they seem happy in the tank then I will keep them rather than move them to sell them as I feel moving them just for the sake of moving them doesn't do them any favors. I would always look into if there were fish coming with the sale of a tank though and enquire what fish they were before buying the tank so that I didn't run into the issue where I would need to possibly move them and sell them.

This is what extra tanks are for.

When buying a used tank, it's not uncommon to find that the previous owner has left their fish behind. So, what do you do with them? Fogerty12 makes a good point that having extra tanks can be useful in this situation. However, for those of us who don't have spare tanks lying around, giving the fish away to a local pet store might be the best option. On the other hand, if you have the space and the fish are a good fit for your current setup, keeping them might be a viable option. Ultimately, it comes down to what you feel comfortable with and what's best for the overall health and well-being of the fish.

I haven't come across this yet however I'd feel bad getting rid of the fish so I would gladly start taking care of them. I don't think I'd move them out of the tank they've grown accustomed to either, unless the poor fish were in harsh conditions. Then I'd clean up the tank, and make sure they have a healthy, clean tank.