It to some extent depends on what those 4 fish are, if they are something as common as Convict Cichlids, you're unlikely to be able to get any ££ for them wherever you go, even store credit varies from store to store.
If they are a much sought after fish you should get something depending on where you go...I wanted to sell my RTM fry to a lfs, but once they found out they were CA cichlids, they just told me they won't have the space. Another lfs was keeping Jags and stated that they have to keep the Jags separate because they were killing each other, meaning they took up multiple tanks, it would be the same scenario with RTMs.
If they have grown near adult size, then the LFS will also have to have room to accomodate them.
I bought a couple of Mayan Cichlids from my lfs, they charged £25..I took them home and they started to cause beef with other occupants, I took them back to lfs after a week, they would give me no store credit for them, but I wasnt in a situation where I could do anything other.
Another lfs (same brand) down the road bought a blackbelt cichlid, again caused beef, took him back after a week and they gave me the same amount I paid in store credit back, cauldnt ask more. Different stores vary in attitudes and current occupants.
I think if you have a pair, try to sell the spares, if not I would donate them to a lfs.