Know your superheroes
Whether you’re a professional selling a product or someone just trying to clear out your attic one of the most important things is to make sure that you’re describing the product correctly. You don’t really need to be an expert on the items you’re selling, but you do need rudimentary knowledge.
In this case, even if you’re not a comic book veteran who can tell anyone what happens in Batman number 365, you do need to be able to tell the difference between Spiderman and Superman if you’re going to sell a costume of one of them. Otherwise, you’re just going to end up getting called out by someone on Facebook who knows more than you.