True- the lying part is lame as shit. BUT- who really cares- as long as you're properly protected by the Paypal shipping policies, what's the difference? You get the money- they get the poster. Isn't that the dream?
I don't offer discounts to anyone who resells, unless they have an established storefront or website, and I develop a business relationship with them. It benefits me to have another website selling my art- they have a vested interest in promoting me, and- they're advertising my name, and I'm getting paid for it. If someone wants to buy my prints to just flip on eBay, then they can pay full retail. There is no added benefit to me to have that happen. (or I should say- not enough of a benefit for me to offer a discount)
Now- the only issue I could see with having someone list your prints on their site and buy them from you when it finally sells- is inventory control- if you sell out of something on your end to your customers, and you don't immediately communicate that to your reseller, then they could end up selling to one of their customers and you couldn't fulfill it. Also, packing and shipping onesie/twosie orders to them all the time eats into your overhead, especially when you're giving them a discount. But that's just my two cents. If it's working for you, no need to change.