Have used Loot for otherstuff but not fishtanks. Could also try Freeads eg
http/household.uk.freeads.net/search.php...orderdirection=
There are a couple of 4 footers there. Could also try ebay I guess or your local paper. Doesn't look like anyone is giving a tank away for free at the mo, but IME you quite often find people on Freeads who're giving stuff away to whoever will collect because they're moving home.
If you're buying a 2nd hand tank, remember to give it a good clean not with soap obviously but vinegar and dipped in one of those dishwashing pads you get from the supermarket will do the job. Then rinse it through. Plus, might want to stick it in your backgarden and fill it with water to check it doesn't leak before putting it in it's final place!
Don't worry too much about the overstocking - sounds like you asked the right questions but just got dodgy advice from your LFS. Plus your dad didn't help! I had the same thing happen to me once. I came home from work to discover my tank had two new residents - both common plecs! They'd even left me a note to say they were just visiting for a while...
Unfortunately (or fortunately...?
) one of them died whilst still a baby but the other grew to a foot long within the first year. I only recently rehomed him becuase I wanted to restock and he would have needed a tank to himself!
Listen carefully to the advice the guys give you here, they all know what they're talking about and if they reccommend getting rid of some fish, even if they're your favs, you should listen. Your LFS will likely take them back, especially when you point out their bad advice.
Good luck!
Ami