I've been (and am) on both sides of the in house/service co issue. The folks who've already posted are correct. There are concerns with training and insurance and also access to the lift companies software.

I've worked for dealers and been sent to work at a customer location who has in-house guys who do not know what they are doing, loved that billing... The few calls you get to the folks who have trained their techs were normally nightmares. They've tried it as per the manual and their experience, and now it's "your the dealer - good luck". Their techs are normally well trained and it's a pleasure to work along side them (most of the time they are dealer techs who now work for the copmpany not the dealer)

I've also set up maintenance groups at large companies. If you can not get adequate staffing or training you may as well outsource the lifts. If you can, then remember that you need at least one tech for every 50 - 60 pieces of equipment per shift i.e. 24 hrs a day with 20 lifts = 1 tech, 40 lifts = 120 shifts = 2 techs etc, as well as a good source of parts and the desire to maintain that inventory. With proper training and support the only time you see the dealer is for warranty work or delivering parts.

I believe that the costs break at the 50 ish trucks/shift mark. Over 50 it was cheaper to do it your self, under it may be cheaper to call the dealer. Good Luck