If I was a machine shop, I’d recommend keeping balance shafts in because I wouldn’t know everything about each engine that comes through. I wouldn’t want to stick my neck out and have an engine come back in 100 miles torn to hell because it needed balance shafts and some idiot kid told me to take them out and now wonders why my “shitty machine work” ruined his engine. So, chances are, that’s why they said they would want to keep them. Risk vs reward. They have nothing to gain by removing balance shafts and potentially a lot to lose if the engine grenades itself.