You cannot trust your Raspberry Pi fully either. In the end you should ask yourself what there is to be gained by the seller, and at what effort, and to what price. If it is white-label, they won't be hurt by bad press. But the larger manufacturers and distributors have a lot to lose. Sometimes the free market does provide some protection.
In the end you should not act paranoid either. But, to be honest, with computers it is hard to tell where you should draw the proverbial line.