Selling pardons for money is inherently a very political act. It means that you are aligning yourself with moneyed interests, which is clearly the heart of Trumpist politics. Setting ideology aside even, the open selling of pardons sends the message to the moneyed interests in general that he's on their side, even if they don't need a pardon at this exact moment. It serves both practical (get rich people to like you and therefore donate money to your campaigns and causes to help them succeed) and ideological (supply-sider-esque doctrine going back to at least the protestant reformation says that rich people should be in charge because they're rich, QED) purposes.