I don't see ebay taking away business from pawn shops. The bulk of the customer base of the pawn shops who is not someone is going to be able to sell on ebay. The pawn shops customers still have a hope of being able to get their stuff back.
The check cashing shops of today is a lot different than checking cashing from years ago when it was mostly a service to customers. Today it is a big business.
IMO the banking issue is representative of the problem. I don't believe it is a structural issue. It is a result of the short term mentality of the banking industry in general. Forty years ago we still had the remains of local companies that served local interests. During the past 40 years there has been a consolidation as companies use acquisition as a growth strategy. It has left large cities, esp. in the rust belt without local access to, for lack of a better phrase , small time capital. Because of the decline of urban education, there really isn't a large source of local entrepreneurs looking for that capital either.
In places like Detroit, there aren't a lot national grocery stores nor are really any small independent grocery stores either. There doesn't seem to will or the capital to create a localized economy.
A 3rd world united states is not going to look other 3rd world countries. It is going to look like Detroit and other rust belt decaying cities.