A wenner is a person wiht no scruples who will employ you to do a job and then after it has completed refuse to pay on the grounds that the work was unsatisfactory. At no time would this issue have been raised before. Further, the work you have done is then used in exhibitions by the person so that they can further their own career at your expense.
'I think I've been wennered', 'is this contract good, or is it going to be a wenner?', 'don't you wenner me on this'