I wouldn't dream of asking hotel staff. I don't use TA as I find it to be very unreliable (although, oddly, I find Google reviews to be more useful but still not great). If I don't know a city, I aim for a nice residential area, away from the tourist and business hotels, wander around and look at the establishments and their menus. I find that works well in more staid cities, but not so well in dynamic cities where areas are changing rapidly. In those places I look for the up-and-coming area and aim for restaurants in those places (eg in London, I'd head to Hackney or London Fields perhaps, in NYC, the Lower East Side, in the Bay Area, I'd head for Oakland. Once you find your area, the rest is easy. I'm not saying that there aren't good restaurants in those cities in tourist-heavy areas, but it's too easy to get seduced by a tourist trap and, even if you can avoid those, you probably won't find the more adventurous establishments.