Here ya go Cleveland (& I'm new here too but not new to this business.) I mark my costumes up by approximately 1/3 of the price. I use the 1/3 and then round to a nice even amount so if I paid $64 and then add in 1/3 it comes to $85.12 so I'd either round down to $85 or up to $90. I do not charge the same amount for all costumes because some have accessories such as hats, spats, parasols, etc. that I couldn't justify costing the same amount but I uniformily markup that amount. I have never had anyone of my students or parents ask if I markup. I'm assuming that they know I do but if they did ask I would tell them the truth. Choosing costumes, measuring, invoicing parents for, ordering, sorting and distributing costumes is an arduous job and that is included in the cost. I wouldn't necessarily volunteer to a parent the percentage of my markup but just that I have to cover my work on it.