thanks for your inquiry
1. As I was testing the site I noticed that when purchasing a membership the "Cash on delivery" option appears. I can't get rid of it. This is bad.
You need set the membership product as virtual product, so it will not need any delivery.
and you can uninstall Cash On Delivery if you do not need it.
Or if you need COD for other product, you will have to make customization changes to hide it for membership.
It is a separated and independent module, our module is not able to control it.
2. Also as a test I tried purchasing a membership even if I didn't have a customer account and it worked. It actually shows in My account > My Memberships Activation date and Expiration date of membership but the account is not a seller!!!
If you want membership for seller only, then please configure the module to "integrated with agile multiple seller module".
By the way, can you tell me which demo site you are using?