I'm not sure how a business goes about dealing with them (if you're interested I can get some info) but for someone like me I would find a scope (or something) I want at your store (which I can't afford right away)and I get a total price then goto the Canex and arrange for a payment plan through them. I take the paperwork to you guys and purchase the scope (or whatever). The canex pays for the item outright and then I have 1 to 3 years (depending on which payment plan I go with) to pay the item back.
It's great because I get the item right away, you get paid right away and there's no interest for me.
I believe the retailer has to pay a certain percentage to canex. Plans are available from $500 to $5000 (I think). I don't believe guns can be sold using it but it should be good to go for accessories, optics, hunting stuff, etc.
I think you would need to contact NPF on base to get things set up.