I have this little idea so when you are out of silver (as I am now XD) and you want to have this pet in the pet trades you can just trade (a pet or item) for it and wait for a message which says your trade offer is declined or accepted :3

 Oh and I forgot to add Breeding Suggestion XD. I'm suggesting you can breed your own pets c:

I like your first idea, except if it was tweaked a little it might work not only when you're out of silver. Add a "negotiate" button on the sales or something? And when you put it in the sales you can have a checkbox yes/no to make it negotiable

As for the second suggestion, it's already possible ._.