Yards can be like that, i moved my old horse off my old yard because of people like that. Sticking there nose in where it doesnt belong. People are probably jealous of your mare. I know someone that put a cctv camera system up in there stable block to try and catch people feeding their horses treats, carrots etc and it worked they then confronted who they caught as their horses are trotters and pacers and were still in work so didnt need the extra fizz or weight.