I can't think of any retailer I trust automatically to only stock good stuff in general. In the UK perhaps John Lewis and Marks and Spencer would have a higher proportion of good quality items.

For specific stuff there are still places like Richer Sounds, I put more trust in them to give me both a quality product and good advice as to what I need, we were downsold a TV from them about 12 years ago which I was very impressed by.

Other than that it's all local retailers, I trust my timber merchants judgement on wood, there's a great little DIY store in town, and a couple of bike parts suppliers on eBay who I know will always come up good.