If I went to the butcher up the road and asked for scraps they would probably say no. If I then said that we used to run a dog rescue and still run a sanctuary and need any free food we can get then they'd probably say yes. It's all down to how much they are willing to risk their business.
I was a bar manager at a very successful restaurant that did a Sunday carvery. They would fill a full BIFFA bin with waste on a Sunday alone. I was allowed to take it away (as much as I could get in the car) because I worked there. They wouldn't allow anyone else to take it for two reasons; 1. Risk of illness and repercussions for the business. 2. Financial loss (I used to eat out of the bin which was emptied off the carvery rack (NOT THE USED PLATES), I know it sounds disgusting but the bins were sterilised and I was hungry. A full 20 litre bin of Yorkshire puddings, beef, turkey, pork, roast potatoes, carrots, mushy peas and gravy). Ok so now I'm hungry just thinking about it :(