For in-store designs one has to define a standard of measurement. In most cases it is no use to design something with the use of only one store. It is preferable to use a reasonable number of stores. Great attention should be paid to the unsolvable problem of comparability between stores. It is preferable to use the more simple research designs instead of the sophisticated ones, because if something goes wrong, and in most cases it does, one need not throw the full experiment away. One should try to design an experiment that takes exogenous factors into account like seasonal fluctuations, trends, etc. It pays to devote great attention to the human factor involved by motivating people who participate, but not too strongly. Rigid field control is an absolute necessity in order to reach honest evaluation.
Selecting points of sales is a problem which many concerns, dealing with large consumption products, have to face frequently, either when they want their products to be sold in first class stores or when they want to start a promotional action with selected retailers or even when they want to launch a new product. Such selection is usually made in their commercial departments which dispose of a network of agents visiting regularly present and potential clients. But sometimes firms needing to make that kind of selection do not dispose of the proper equipment and they have to call in external sales forces or research companies. Sometimes ago, I had the opportunity to take part in an experience which I think would be interesting to be reported here. With some improvements and adjustments, it can be applied to other cases. At first I shall try to report the problem as it actually occurred and draw the main lines of the method and then I shall give the main results that were obtained.