Living in London, I tend to follow one of two patterns. Either go to a part of town known for some large department stores, eventually navigate to the right bit, and pick the option that's most appealing from the smallish selection on offer. Assuming they have anything to choose from... There's a famous place that I now refer to as "Never Knowingly Stocked".

With the Amazon option, I've already tried several search terms to get an idea of what's available. I look at sales rank, and click on the link for "best sellers in category". I have a few browser tabs open for different product options. I read reviews... three stars first, then work my way up. (I seldom bother with the one-star reviews, because you have to filter out the batteries-upside-down no-hopers). I usually have a tape measure handy if I want to double-check dimensions. When the choice has been whittled down to two or three alternatives in their own browser tabs, I'll have a quick look on YouTube to see if there are any reviews, and to get a feel for how it operates in practice. Finally, I might have a quick check on eBay to see if a cheaper price or quicker delivery is possible.

If anything I think I'm putting more effort in, spending a similar amount of time as the trek to Oxford Street would take, but arguably sourcing better stuff.