On a business trip to LA about 15 years ago (ironically to meet with the LA Times IT team), my colleague and I arrived to town early and decided to get lunch near Koreatown. We came upon a stripmall area with several local restaurants that surrounded a parking lot anchored by a larger Staples store.
We found a parking spot and noted a nearby sign saying that parking was reserved for customers of the local businesses. We thought nothing about it as we put our laptops and bags in the trunk then went around the corner to check out the 3 or 4 restaurants on that side of the block (they were obviously part of the businesses attached to the parking lot.)
We had a quick lunch at the cuban place on the corner only to return to the parking lot and an empty space where our rental car once was. Elapsed time was maybe 15 mins.
As you can guess, the cuban place was not part of the approved parking list and they paid people to watch and follow people like us who park there illegally. They quickly summon a waiting truck who swoop in and tow you away. We were forced to wander west LA looking for a cab and then pay extortionist fees (I think it was around $400 bucks) to a shady tow company in order to get our stuff back.
Lesson learned the hard way. Always read the signs carefully.