The work in this paper presents the study of the influence of a particular environment on the performances of passive UHF RFID tags attached to products presented in a retail store. The effects of the near-field environment and of the far field environment are successively and separately highlighted by comparing the results of measurements carried out in different kinds of configurations. Those configurations are respectively the case of a tag alone, a tag attached to an item, 600 tagged items arranged on shelves in an anechoic chamber and then in a real store. This approach reveals a similar behavior of groups of tags which could enhance the detection even when placed among hundreds of others. Free Space and 2-rays path loss Models are used to show that multipath may be profitable for the link budget in realistic scenarios.