Stan is a financial advisor to Wade Gustafson, who tells Wade that the real estate deal Jerry is bringing to them is actually a good one. However, they just want to give Jerry a "finder's fee" without letting him in on the actual deal itself.
Stan appears at other points in the film as well, discussing how to approach the kidnapping situation with Jerry and Wade. When talking with Scotty, Jerry justifies his decision not to call the police by saying that even Stan agrees with him. So Stan's seen as a sensible and smart guy by the family.