I've got some time in Lake amphibs.
You'll be hard-pressed to find one that hasn't had at least one incident with dragging a pylon or catching a wingtip during high speed step-taxi. It's an airplane, and just like an airplane or a boat, it wants to bank in a turn on the water, when step-taxiing. Unfortunately, unlike a boat, it has long wings which can't be allowed to bank during those turns. Catching a tip isn't uncommon, and can result in structural damage, as well as corrosion issues.
Corrosion issues are also an...issue.
Get a good pre-buy inspection, if you're serious.