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Yeah, the likes of Wickes etc do have a high domain authority but they're not focusing on these specific search terms. They are appearing because they are closely related. If they did focus specifically on each search term I'm sure they would be number 1. I'd suggest building up your long tail, maybe slightly varied to your competitor so that you do trump them at the top and just continue down the path of progression. They've probably been there a while and Google has no reason to shift them if people are clicking onto their site and finding what they want.