Besides referrals you should also consider asking the dealers or OEM’s directly what the machine/technician ratio is in your specific area.
For example, if one dealer has 1 tech for every 10 machines in the territory and another dealer has 1 tech for every 40 machines, you should consider how this going to affect the service response rate.
Response rate may also be affected by type of account. For example, if a dealer has several clients with multiple sites and you have only one, the service queue may occasionally become preferential.