The first question you ask assumes that shopping at competitor's premises – presumably to gather competitive information may involve unethical practices. In this, of course, you are correct. As a consumer, there should be no problem shopping at a competitor's outlets. However it is certainly not ethical to nose around in "staff only" areas or store rooms, for example, or to damage stock, etc.

You ask about making lists of prices and stock. This is almost certainly both legal and ethical. The information is public - and so there should be no problem here. Of course the store staff may object and ask why you are making long lists of prices and stock holdings. If they do, you would need to say what you are doing - otherwise you would be misrepresenting yourself. They could ask you to leave - although they could not object to anything else.

Using a tape-recorder, however, is less straightforward. If this is for your own purposes - for example to record the prices rather than write them down - then I can see no objection. In fact you may find that it is easier to record prices / stock on show using tape-recorder. (So long as you don't mind people looking at you as crazy for talking to yourself). However using a hidden tape recorder to record the sales skills or dialog used by sales people is suspect and a grey area ethically. (In fact in some markets, recording people without their permission is illegal).

It is a normal competitive practice to benchmark competitor prices. Most major stores have people who routinely check competitor prices. In the UK, if you go into some big supermarkets you will see sample baskets on display with the supermarket's own basket claiming to be the cheapest. (If you buy this from us, it will cost so much. Our competitors charge this for the same goods....) One store (John Lewis Partnership) even made claims on their web-site to employ people with the job of price checking - and they offer staff bonuses to spot prices cheaper then John Lewis prices.

If you are not monitoring competitor prices then you are missing a crucial and readily available source of competitor information that can give clues to a vast quantity of additional data. (Link price changes to company financials, to get trends in profitability; price changes also gives indications on how the company sees its products over time, and thus overall marketing strategy). This applies irrespective of whether you are a retailer, manufacturer or in a service industry. The only real difference is the accessibility of the price information.