I've only ever promoted Amazon products as an affiliate and not as a seller. I find it easier to get sales from the UK market, as the keyword competition seems to be less competitive then the US market, but there's the £7 commission cap on the UK program.
I promote technology products like LED TVs, tablets, home cinema systems via the UK program (£80 - £400) and fitness items like treadmills, elliptical trainers, exercise bikes via the US program ($500 - $6000). This approach has worked well, but review blogs don't seem to be ranking as well since the recent batch of Google updates, so I've switched to You Tube slideshows.