If you are regularly doing large projects (over $100k) then I can see partnering with a finance company to work something out where you get paid in full, and the finance company takes the risk. But I don't see the reasoning in offering financing for things like wraps etc. If a company can't afford to pay you $3-4 K today to wrap their van, why would you think they could pay you in a few months?
We offer some long term clients net 30 terms, that is the extent of our credit. Knock on wood but we have been pretty lucky over the years with it, only been burned a handful of times.
I'm blown away by how bad some companies are at the financial side of business, I've had companies come in to pick up small orders of $2-3 hundred dollars, give me a cheque and ask me to hold off till the end of the week to cash it, how a business can operate with less than $300 in their bank account is beyond me, but I see it on a semi-regular basis, on this fact alone I would never offer to self-finance projects.