I think we can benefit from taking a leaf out of Super User and going with a "No Shopping Recommendations" clause in our FAQ. And I like quack's take on the subject - we should be fielding questions not about buying strategies but on technology strategies. For example, see another graphics card question over here.
Buying strategy in itself is a compound of two concepts - getting deals and getting the right equipment. The former is all about money and falls under localization issues of changing economy. The latter is exactly the kind of thing we can, and should, address. And the thing is, when you aren't actually looking for prices and shops, any "buying strategy" question can be isolated from the actual concerns of buying them to focus on the actual differences:
Almost any real-world buying advice we will be fielding will be on hardware and software - just use those tags to cover the subject matter. People who want to look up information on graphics cards should be looking for information on graphics cards, not purchasing strategies. I think the tag is unnecessary, as such, for these questions, and actually potentially dangerous to our site's survival. Just like the [subjective] tag (incorrectly) implies to people that subjective questions are allowed, this kind of tag would promote people to turn the place into a site of shopping recommendations. We're better off without it.
Likewise, I don't think we really need a 'buy' tag for comparing prices in-game. These things are probably better off tagged with whatever inventory is being sold in the shop. A question like "How can I get the best price on Pomello Juice in SO3" doesn't really need to point out that you're buying it. People are more likely to find these kind of things by searching the actual item they're looking for and comparing, not with a [buy] tag. So I say we get rid of it completely until we actually stumble across a question which actually is about some core buying concept.