Any service managers or ex service mangers?
Giving a tiered bonus based on sales helps with up-sales and efficiency.
I manage a GM body shop and while not the same you could do something similar.
150k/month = 2% of gross sales
100k/month = 1.5%
90 and below = 1%
I also paint every vehicle that comes through the shop. I get paid flat rate for that as well. Our refinish efficiency is around 250-300% and body is around 200%