Obviously people shouldn't be able to create as many credits as they want willy nilly ... Someone would only be able to create a small amount at the start, slowing building up trust with the system through payments back to it ... Not sure what algorithm could be used for "trust building".
Algorithms for this "build-up of credit" have been well-developed by various LETS schemes over the years.
But these schemes necessarily depend on tying credits to the identity of a specific person. There's no possible way to combine your idea with a pseudonymous block chain like Bitcoin.