Everything I can buy on Amazon, I buy on Amazon; everything I can buy "Prime + actually sold by Amazon", I buy this way, even if it's a little more expensive, because I know it will arrive on time no matter what, and I can return it with zero hassle.

There may be a micro niche of price comparison within Amazon, because some rare / specific products are sometimes sold at wildly different prices on Amazon (and listed many times; not just different prices under the same listing).

And of course Amazon's search engine is completely broken; an actual product search, limited to Amazon, that worked would add tremendous value.