You are never forced to activate mana abilities to pay costs, so if there is a mandatory additional mana cost (such as from Thalia, Guardian of Thraben), you can decline to activate mana abilities to pay for it and hence fail to cast the suspended card, leaving it in exile
For example, you can add some soft light reflections to a certain spot to show that the sun is shining brightly onto it, or you can make it look like the light is being diffused by the humid air
Gilanra, Caller of Wirewood + Brinelin, the Moon Kraken is one of the more underappreciated pairings, but they have the potential to be some of the sweetest Timmy-style value commanders in Magic
Simply set a price for your collection at a point that you perceive to be slightly above the market value of your cards, and then let Mercari incrementally drop the price until a buyer pulls the trigger