The E-ticket FAQ includes this item:

Can an attendee buy a E-Ticket from me the Event Host?

Yes, if they have a valid payment method on-file in their Gen Con account, the smartphone app will prompt you to sell them an E-Ticket.

The reason for asking is that there are two discussions on the Friends of Gen Con FB page concerning someone getting ahold of a person's badge barcode (maybe from a pic of the badge posted online), then printing a fake badge with that barcode and using it to charge events to that person.

Is that even possible, since there doesn't seem to be a way to save a payment method?
 

No one can tell me how to put a payment method on to my account?  I may actually need this as I plan to attend an e-ticket event if they have space, and would like to see how this works.

Every time I've bought something, it makes me re-enter my CC info.  Normally, it's already there, but I thought that was Chrome auto-filling the fields.  So, the CC I've used to buy badges/tickets is saved?  That's good, but it would be nice if there were a way to view what's on file, and update it without purchase.  Please add it to the to-do list. :-)

How do I change it now? There should be a way to see what payment method you have stored, so I can delete or change it.

i honestly am not very comfortable with not having access to it with out having to purchase something. 

It’s the first year they’re doing the purchase-on-the-fly option, so they need to work out the kinks.