This happened 14 years ago and was so terrible that the DM still curses us. A little forethought, this was shortly after high school, we would go to one of the local shops and play 3.5 in the back room because we were allowed to smoke there and wouldn't have to take breaks every 30 min or so.
There was a party of six of us, the DM had each given us the choice of one item that we could have within reason. Our Paladin got a cloak of Cha, she was very persuasive and was worshipping the deity of hedonism, we had a rogue, a ranger amd a monk whose items I have since forgotten, our barbarian had gotten a Maul that every time you killed someone with it, it would increase in size (sounds cool right? eventually it becomes too large to wield). I was playing the only dedicated caster, a wizard, the only item that I wanted right off the bat was a Belt of Many Things(its essentially 64 small Pockets of Holding, not overpowered).
We had been on a couple adventures and the Paladin had been doing her Persuasion things, including on the party (which was kind of uncomfortable because all of us were guys), being the only one in the party with good sense motive and Will saves I was pretty much immune to her charms. The Barbarian had gotten 2 killing blows with the Maul so now it was Huge.
We come into a town, first thing I do is say I'm heading to the magic shop. Get there, ask the merchant about the belt, he says has one but is not willing to sell it. I get pissed off, storm out and start plotting on how I can get my item. That night the rogue and I go out and scout the shop, it warded, of course. I start taking my time looking for weaknesses, nat 20 on perception. DM says that the foundation is not warded or magical at all. LIGHTBULB! I send the rogue to get the Barbarian and his maul.
When they finally arrive I instruct the barbarian (whose Int was 6, gotta love dump stats) to swing his maul underhanded at the foundation at a very specific spot. On the third swing the shop collapses. We immediately start searching the wreckage, I grab the belt, put it on under my robes, pull out a potion and feed it to the owner right after we dig him out.
At this point people had started to gather around wondering what had happened. When the guards approach they ask what happened, I immediately speak up, saying that I am pretty sure that it was a localized earth tremor under his building from the shear amount of magic that surrounded the building. (Bluff check, nat 20) Guards nod in agreement saying that it makes sense.
Rumors quickly spread throughout the town about the band of heroes that had miraculously saved one of the most important people in town. We were thanked and had a banquet thrown in our honor, the Townsfolk also had a master stone shaper make a monument in our honor. Through all of this the shop owner had no idea what happened to his inventory. I convinced him that the amount of warding and protections on his building had messed with the extradimensional spaces that the belt contained and the ensuing explosion must have destroyed it and everything inside of it.
We left town a day after the feast. That night when we break camp I start emptying the contents of the belt. When all was said and done, tallied up just under a million gold worth of items. We were level 4 or 5 at the time. The biggest caviat to the sheer amount of items is that no one nearby would be able to buy more than one or two items at a time.
Just goes to show, some creativity and a little luck can break a game. I suppose we did take the saying "Knocking over a shop" a little too literally though.