The original problem was simply "I want to hook up a photo and my paypal account easily, so I can share the link with friends and sell my (physical) stuff".
As you've touched on, I really don't want to get into payment processing myself (messy), even though it would be a simple path to revenue generation. I also don't want to charge people outright for using the service. I think this is way more casual than regular e-commerce, I'm not going to take a % transactional fee and/or a monthly fee just so a girl can sell a pair of shoes she doesn't wear.
I figure that with enough mass there will be other opportunities to generate revenue by upselling services to help people extract more value. For example more visibility - if there's something you need to sell urgently, pay $1 and it appears on the top for a given locality / tag.
I'm not really concentrating on building mass yet though. It's still very much in the MVP stage - right now all I want to prove is that I can help people sell their stuff. Need to get that right first.
Thanks for the inspiration. I need to do this.
Admittedly I've only recently begun using PayPal for selling so I'm still a bit unsure about how they handle some scenarios.