For some customers being rude comes natural. Still others lower themselfs and make being rude a bit of a game or their own form of art. I personally have no time to squander on accounts like these described by the OP. I trust my judgement and fair play
on this matter. Mutual respect and consideration by both the vendor and the customer is key. If neither is possible purge the customer from your business and move forward.
Don't waste valuable emotional capital on accounts that live to pull your strings
or think they are in control.