We adopted a 2 1/2 year-old black lab/hound mix Heidi and a 1 1/2 year old same breed Sadie. Both have issues. Heidi has treat aggression and it took a lot of patience to work through that. It's not 100% but she only growls at me when she is in the moment right after she has killed a rat. At least she will trade up for a Greenie. lol
Sadie is an unbelievably independent dog. She knows her name but does not always listen when called. She is a sweet girl though.
I think you can get a feel for the dog at the shelter. (I go by intuition a lot).
We were looking at another dog, and the shelter worker advised against it. Saids she was a bit "off"