Trenchers rarely has locals visit it because it is hellish expensive for what is basically fish & chips. The place is run solely for the tourist market.
If you want fish & chips to takeaway, all the locals use The Railway Chippie which is about 4 mins walk from the train station. If you want directions, let me know.
For meals out (NOT fish & chips) I recommend the Moon & Sixpence on the west harbour side, or The Red Chard (brilliant steaks) on Flowergate. For bar meals in town I recommend the Resolution Hotel on the corner of Flowergate/Skinner Street.
If you fancy an Indian meal, go to the one situated in the train station and NOT the one over the road (I've seen the kitchens - gross!)
For a chinese meal, the restaurant attached to the Metropole Hotel on West Cliff is the best one.
Other restaurants I would recommend you AVOID (due to personal bad experiences) are The White Horse & Griffin (Church Street), Greens Restaurant (Bridge Street) and Bagdale Hall on Bagdale.
Finally, a word on the world famous Magpie on the pier road. The fish & chips are good but again, very expensive for what they are. Plus, you will have to queue.