1eyefishing
...just joking, seriously.
If I sell a boat, do I let the tag go with it or retain the tag for my next boat trailer?
You keep your tag. As an aside, if the next trailer you purchase or register is a light duty trailer, look at a permanent tag. I just got one for a new 5X10 utility trailer. Think it cost me about $40 but in future years I only have to pay the Ad Valorum fee and not the standard tag fee.