You don't need to be an A.C. Moore Marketplace member in order to purchase from a seller.
You can simply checkout as a guest.
How to checkout as a guest
Once you've added all of the items to your cart that you wish to purchase, click on the "Proceed to checkout" button.
On the next page, you can just continue to fill in your details to complete your checkout. If you have an A.C. Moore Marketplace account, you can follow the prompt to "sign in", but this is completely optional.
You'll receive the sellers' email address in your purchase confirmation email, so if you have any questions you can email them directly.