I tried a bit of tutoring, not a scam like some others are. They genuinely gave lots of tips about my performance, set things up in a way that was realistic. By that I mean they'd ask a challenging question, ask you to work through it and give you tips when you're stuck, like in the actual interview. But I think it helps more in the sense of helping you get used to working out loud (you could practice that yourself I suppose?), working with hints and keeping going, but NOT to prep for the questions they'll ask you, because it'll almost certainly be different from what you did, there are just too many questions to choose from. So basically more Oxbridge specific interview skills but not making you 'smart' enough to make it. They're also very expensive, of course to take advantage of rich people who are who wouldn't mind forking thousands for a better shot.