I'm not really sure what to do about this tbh, because I've got plenty of examples that are easy to access. I work in traditional art + am very broke, so I make it a policy not to commit to a sketch/commission unless it's been confirmed because my supplies NEED to be paid for/kept fresh. I don't ask for payment up front normally (what I do is confirm the commission and either take 50% up front and the other 50% after the sketching process is done or take the full amount after the sketch is confirmed), but this is a really big order and it WILL eat up a good chunk of my inks/markers, which will need replacing, as well as paper and pencil lead (both of which are thinning to the point of needing replacement soon).
One person has suggested I take a down payment - not necessarily 50%, but a fair percentage - before sketching anything so if they do choose to take the sketches and finish them themself or have someone else finish them, I'm not losing out on supplies and time, while another says I should just do the sketches and if they choose to take them and complete them a different way, that's their choice. But IDK I'm not terribly experienced with big commission projects like this so I really could use some advice. :(