If you were to get a motorclub call and a retail call at the same time and only had one truck available for the next two hours. Which call would you take? 
They both have to have you there in a time period that requires that you send the truck right now. 
Neither will accept an extended ETA. 
What if the motorclub call came in ten minutes after the retail call????
What if the retail call came in ten minutes after the motorclub call????
I generally operate by the rule of first come, first served. If I accept a call from anyone, MC or retail, it gets taken care of. I would prefer to refer the second person to a competitor than to damage my reputation by cancelling a call I had already accepted simply to take a different call.
Now here's the caveat. If the first call was a MC that used me as last resort and I didn't care about them (let's call them USAC lol) I might cancel them if something better came along and I couldn't do both.
Agreed!