Surely they're reselling at far lower prices than they're listed in stores (otherwise who would buy their stolen goods), which forces then the official price for that product to go down in the area, in order to retain shoppers.
For example, there was a time when my cornershop guy was selling 12 packs of Coke for £3.50. I didn't ask where he got them, but I definitely stopped going to my local Sainsbury's for a while (which is currently selling 4 packs for £4.50).
The thief got a cut, the cornershop guy got a cut, and the savings were passed on to me. The retailer's stockholders lost some minor value.
I fail to see how this is not a rebalancing of prices.