The way watering cans sell when you have multiple seems broken. The more you have the higher the Sell All option is. However it does not sell all of them, just one use per can you own by the looks of it. It gives you gold like you sold them all though. Maybe I am missing something here.
the creator of this game made the tool having durability instead of craft a large quantity of tools, it means if the gem cutter has 5 durability, it means it crafts 5 gem cutter using same material before
and probably the creator want to make watering can profitable ( 2 plastic pellet for 4 watering can use equals 6 = 64 ) so it's little overpowered in early game but no if in late game