My first private purchase 30+yrs ago.... you know, a friend of a friend of a friend had a pair of discus for sale. The drawback was you had to take the whole tank setup. I thought about it then went over to check the fish out. Nice big pair of blue turqs with 22 young about an inch and a half. All looked to be excellent value so I gave him $400 as a 50% deposit while organising to return next week to pick the lot up. When I arrived with a couple of buddies to help out, all the fish were already in buckets (no airstones) and the tank was empty..... Excellent start I thought as it was a bit of a drive home. We packed the lot and left for home.
Obviously (In Hindsight) the fish were very stressed. No young survived the trip. The adults went straight into a quarantine tank and sunk like a brick even after a good acclimation went dark black and died 12 hours later.
I rang the guy up and asked wtf did he do when emptying the tank or what ever......
He replied - "My wife convinced me it would be of great help and assistance if we removed the fish & water the night before"
NEVER LEAVE FISH IN BUCKETS WITHOUT AIRSTONES !!! 
NEVER LEAVE FISH IN BUCKETS OVERNIGHT !!! 