Golem reportsthat an employee of an electronics store stated in an RTL documentary that jamming transmitters are used so that customers can no longer easily compare shop prices with Internet prices. Personally, I think this is a bold thesis: although some shops may not exactly favour mobile phone reception because of their design, real jammers would be too risky. The image damage if such information turns out to be true would be too great. On top of that there are legal problems, you can't even operate a mobile phone jammer without a license.
Mobile online price comparison is of course an unpleasant possibility for consumer electronics stores. Often customers will want to haggle on the basis of Internet prices - which is also favoured by the corresponding advertising. Smaller stores can score points with good advice or offer products that cannot be easily obtained online. However, the big players in the industry usually do not make use of this possibility, the advantage of the shop is not immediately apparent to the customer and therefore similar prices are expected.
One legally used possibility to make price comparisons more difficult is to slightly change product names (which may also require other functions). This offers two possible advantages: if both product XY 1234-A and product XY 1234-B are available, this not only makes it more difficult to compare prices, but also to find the product test. The latter is important if the minimally different designations hide significantly different products.
The battle between shops and the Internet will continue - whether technical measures in shops will prevent the use of mobile phones is an open question. Perhaps some markets are actually so desperate that they are considering such solutions.