Does a product become forbidden if it is stored for a day or two in a shop that may have been established with illicit money?

The prohibition (haram) is not related to the money itself, but rather to its characteristic and the owner's liability. So, if the characteristic of the money changes, its ruling changes. If a shop were established with ill-gotten money, the prohibition would relate to the earner's liability and the characteristic of his earning, not to the shop itself. Consequently, the goods stored in this shop would not be subject to prohibition, even if there was a prohibition related to the owner's money. This differs from a case where the shop is usurped, in which case it is not permissible to use it for storage or anything else.