Yesterday there was a question about small commercial rocket motors for sale in the U.S.. I'm going to post an image of it in case it becomes inaccessible in a while due to deletion:
TildalWave put it on hold on the grounds that there is a policy across SE against questions asking for a shopping recommendation. The argument is that any answer becomes obsolete quickly, is highly dependent on the particular needs of the asker and as such is usually not useful to others, and that if recommendations were allowed, attempts at covert advertising through fake questions and answers would immediately appear.
The question had been around for a number of hours when that happened, had received two answers, and nobody had noted the shopping issue and flagged, commented, or voted to close. In my case, I just wasn't aware of the entire issue.
Rikki-Tikki-Tavi had answered with a brief relevant list and made the case the rule doesn't apply here:
...I don't think it's fair to say that he's asking for a product recommendation. He's asking what companies manufacture these. Also, most of the arguments why product recommendation questions are bad do not apply to SE. Most of these thrusters were designed decades ago with minor upgrades (so why will they be obsolete next year?), personal preference is not much of an issue, prices are unavailable in any case, and he explained that he wanted US manufacturers first.
It is certainly easy to see why it seems doubtful that vendors or buyers of spacecraft components would use Space.SE to boost sales, or would be influenced by opinions here. Or is that entirely true? One doesn't get the feeling the asker was actually about to buy a rocket motor, because if he was, it would be very strange if he didn't already know about the market. Is that going to apply to all commercial components at all times? Can it be handled case-by-case since it seems unlikely to come up more than rarely? Is it viable to make a complete list of all products to answer such questions and have confidence it won't become obsolete?
There was enough debate on this occasion it seems to deserve examination. Since I am pretty neutral and also am trying to get used to how to handle all this kind of thing, I decided to do the asking.