Know when your machines are in heat, and keep them separated (in a well-lit room) to prevent unintended growth in the herd.
Avoid the temptation to wander through strange yard sales, new thrift stores, or Craigslist ads for your (or adjoining) cities.
Look straight ahead, with both hands firmly on the steering wheel, when driving through residential neighborhoods on “trash day”.
Do not let anyone know you collect, repair, (or even use) old sewing machines lest you become the local foster home for wayward and orphan units.
Have a “sponsor”, who you can call for an intervention, when you start to think eBay is a good place to find affordable, high-quality, “industrial-strength” vintage sewing machines (that will arrive at your home completely undamaged.)
Learn to say “no, I’m stronger than this” if you suddenly find yourself climbing up on a dumpster behind the local Goodwill (in your Sunday clothes) because you thought you saw the LBOW colors of a vintage Singer peeking out.