We solved the problem years ago by instituting two interlocking solutions. First, I see no difference between pirated software and licensed software that the user decides to not pay for. In both cases, we took advantage of ubiquitous Internet connectivity: we require an active Internet connection to run our software and one of the principle purposes of the Internet connection is to handle accounts receivable issues. Latency varies with the package and the customer, but none will run six weeks without it being OK with us. The client recognizes, in writing, these facts at license time (one of those pesky highlighted "sign here" blanks), and agrees to the terms and conditions of the license.
The last real problem was with Foley's, a department store chain, in 1984, and that was because we let our sense of humor overcome better judgement and embarrassed a middle manager. Now, the "automated collection system" is very subtle, but continues to be very effective.