The problem was not with the seller, but the product itself. When I received it didn't switch on at all. One of the battery wire wasn't soldered . I soldered it after opening. Now it's working well. Sorry, bad quality of the product assembly line. Please take this into account when somebody order this kind of product . It's chip one with a low quality but finally it works.
So far so good, a nickel weighs five grams and they calibrated correct on 1000 grams.