Whether it was the intent or not, the preference is that using Cheat with Steed/Ship Enhancers that have GP values is a silly practice, in the positive sense. In other words, it's allowed because it's silly in a way that's not going to break things, cause people to end friendships, allow for world peace to get in the way of anything, etc.
Since I never said that Ship Enhancers and Steed enhancers weren't Items, I'm not sure where it could be inferred that you couldn't sell them, and I guess I can't see a reason why they can't be placed on the table as a carried Item. The only reason I would say no is that under normal circumstances, there's the weak implication that they should be placed behind a Steed/Ship card when played, but like I said, that might be a weak implication.
As for trading, well, that depends on if the Enhancer can be put into play, and whether it's already attached to a Steed/Ship or not. If it's attached, then there's no way the answer can be yes, at least for the Enhancer itself. Steeds and Ships can still be traded, I believe, under Item rules (you might want to double check that, though), and any Enhancer would go with it.
So, here's what is going to be considered official:
- Steed/Ship/Hireling Enhancers with a GP value are special Items, but they are still Items.
- Given the above, they can be played to the table and carried, even if you don't have a legal way to use them (unless the rules or cards say otherwise).
- Given the above, they can be used with with the Cheat! card.