5 credits aren't that much depending on the vehicles you sell me. In fact, you can give vehicles you already made. I have to build custom-made vehicles and that costs labor. That's also why I give you a discount if you're fine with something I already made (3 credit discount).
First of all, they'd have to order a premade vehicle for me to resort to vehicles I bought. Second, I'd check with the creator of the vehicle if it's alright if I sell it to someone else. OR, if you sell a vehicle to me, you can give me distribution rights to it, if you choose this, then I'll give you extra credits. (But only if I want distribution rights)