It's fiction. What matters is if you are able to suspend your disbelief and enjoy the story. It sounds like the premise didn't work for you. I often avoid books about things I know because of that issue. I read a lot of crime fiction though, and have a lot of gun knowledge, and often find myself wanting to throw the book across the room.
I'm enjoying it so far but the plot seems to revolve around the idea that someone stole a trailer full of horses to sell to slaughter.
That just seems a bit un-realistic to me. Does it actually happen?
It can... I had a trainer that went down to Arizona to the winter shows. Dropped the horses off and then went to check in to the hotel. Came out and truck/trailer was gone. Found it a few days later in the Mexican desert with a couple hundred miles added. If they horses would have been in there who knows what would have happed... maybe they would have never stolen it, maybe they would have sold them to the highest bidder or let them go in the desert... who knows?