I wrote the blurb on the off-topic page a while back so I would not have to keep justifying the policy, since I think it requires justification and -- yes -- to provide people with a way around it while leaving what I see as the real intent intact.
Originally it simply read:
Please note that the following is off topic:
- Asking for specific purchasing recommendations.
Before I explain my goal here, I'll explain another related convention that's been enforced as long as the site has been around, I believe: If you are endorsing/promoting a product (hardware or software) by recommending it in an answer and you are the creater or retailer of the product, you must be honest and disclose this.
So, for example, our #1 ranked user is the author of pigpio and doesn't try to hide the fact, etc. This is fine and good.
However, occasionally people spam the site by posting a bunch of answers to questions where they recommend a product as a solution but do not disclose they stand to profit by its use. This is not so good in terms of a slippery slope to just allowing people to more-or-less use us for free advertising and so we have a policy whereby we can delete those postings.
The "no shopping requests" as I understand it is mostly there for the same reason. However, there are also a lot of potentially useful and valid questions about using products (we are, after all, a site dedicated to one). But, because you cannot just ask, "What power supply should I buy?", the most obvious way of being sneaky, asking such a question with one account then answering it with another, is cut off.
It also means we do not have a 3 year old question, "What power supply should I buy?" with 50 different answers added over time from different online retailers -- who, if they sell other Pi related products, could then go look for the "What case should I buy?" page and the "What wifi adapter should I buy?" page and the "What touchscreen should I buy?" page and so on and so on.
There's a further objection to that kind of question, namely that they are inevitably primarily opinion based -- which is why we don't allow for "What OS should I use?", even though it is not a shopping request.
Combining those two rules, it would be okay for someone selling a product to ask, "Is this power supply okay?", and then answer yes as long as they disclose they are selling it. As far as I know though, no one has bothered to do this which might be taken as evidence of the fact the policy is dissuasive.
The other thing I'd add about "What power supply should I buy?" is that it is really a question for a search engine, and there is no need for people to ask others to do that for them. At the very least, the policy means that someone must make an effort to do a search for a Raspberry Pi power supply, find one they would be willing to buy, and check here that it is really okay.
Occasionally people claim they tried to search for e.g, a microphone input but could not find any. Giving them the benefit of the doubt, the issue is either the search terms they used or that they do not understand, in this case, that pretty much any $10 USB sound dongle will work for exactly this purpose, which is why it is okay to ask "What should I look for?", which again perhaps requires slightly more effort than "Give me some product page links", but probably will produce a Q&A that is more generally useful.
This is why I made explicit the two ways around the rule -- which is how it was being enforced anyway. I think this is somewhat friendlier and more productive than just closing the questions with a link to a help page that says sorry you can't do that. Instead I'm inviting people to think a little bit, and, in the end, hopefully get help with their problem.
Now, instead of the initial bad question, we get an even worse question
I'm not disagreeing that this is possible, although it would have been good if you could find an actual example of such. I can't remember having seen one.
I would disagree in the sense that I think the normal trajectory is from a bad Q&A:
- Q: "What power supply should I buy?"
- A: "Buy this acme one"
- A: "Buy the official one"
- A: "This is the one I have, it's great"
To something which is somewhat better:
- Q: "Is this power supply okay?"
- A: "No, it does not provide enough amperage"
Etc. Notice again the first form is, in a context where the answers are upvoted and accepted, almost inevitably subjective/"primarily opinion based".