Revenge without violence or recrimination is always my favourite method. Patience (something I'm not good at) is important, because the longer it takes before you choose your moment, the less chance you'll have of becoming a suspect. Two examples:
In 1979 I had a 1972 Mazda RX2 coupe (which I wish I still had, they're worth a fortune now) and the 12A engine schidt itself. I went shopping for another car, and bought an ex-Victorian Police 1967 Ford XR Falcon, my first of many Fords. I bought it from a shonky car yard for $1000, less $400 for the Mazda.
My then arsehole of a brother in law to be was a cop, and he took it upon himself to check it for safety defects and found a few, so sent me back to the car yard to remonstrate with the proprieter. The long and the short of it was that we had a big argument which almost became a punch up, and I got no satisfaction.
That was around July, but I purposely didn't seek revenge until around December (summer time) when I returned one warm evening with a "Super Soaker" style water pistol with a capacity of about half a litre, and range of around 30 feet. I'd filled it full of brake fluid, and was able to spray it onto the first two rows of cars on that occasion, and on two return trips (several weeks apart, never return to the scene of the crime too hastily) I managed to get the more expensive cars that he'd parked further back from his front fence by cutting across the railway line behind the premises. The proprieter did a lot of "Jam Jobs" (quick resprays) using spraying enamel, and the brake fluid lifted this stuff almost on contact.
Years later, I bought my first BMW R100RS. Sadly it was a dud, and the big end bearings were shot. The proprieter eventually agreed to fix it, but I had to pay for the parts and he'd pay for the labour. Sadly his mechanic wasn't aware that BMW boxer conrods have to go in with the oil holes facing down, and of course he didn't, so the new bearings were destroyed by the time I got home. I came back and of course the argument got nasty, and he suggested that I sue him. Fcuk that.
After a few months I visited the bike shop early one Saturday morning and poked tooth picks slathered with superglue into both of the front door locks and cut them off flush with the lock. They had a side entrance for their workshop and staff entry, so it got the superglue treatment as well. I went for a ride (on my other bike) and came back around opening time, and bought a coffee at a shop across the street, and sat and enjoyed a coffee and a cigarette as I watched the entire staff and customers milling around the front of the shop while a locksmith drilled out the locks.
Once again, I did this a couple of times, several weeks apart. They had installed CCTV, but motorcycle helmets are excellent disguises, and I owned several helmets anyway, so I never had a visit from the police. They say that "Revenge is a dessert best served cold", and I couldn't agree more.
I could just imagine the arseholes that ran both shops trying to go thru their mental rolodex of all their unsatisfied customers, unpaid suppliers, disgruntled staff members, etc etc, which must have pissed them off.