if anything, a free custom can be good practice for if you ever DO want to do customs! i love your designs, but i also get the custom experience and the adopt experience are totally different things. there's a certain level of pressure to making sure the client gets Exactly what they want - so without any actual money being exchanged, it could lessen the pressure? i'm just spitballing ideas though LOL if it's too far out of your comfort zone, then you don't have to do it!