Pet Lending is where you can safely lend one of your pets to another player without fear of it not returning. You can only sell your standard pet (pets that are not limited edition or restricted species) by Pet Auction. You can trade pets at the Pet Trades or send them permanently at the Pet Exchange.
If the player accepts a pet you lend them, they will have to pay the MP fee below, which is the sending and returning fees. Any pet that you lend to a player will automatically return to you by the time that you select below. You cannot receive it back early unless the player lending your pet sends it back early.
While the player is lending your pet, it will be safe from any change in a special Nimbus cloud.