I have a 2005 19' Keystone tandem axle travel trailer and (yes I know) never serviced the axles. I pumped some grease into the zerks every few years, but haven't repacked the bearings or adjusted the ...
I would also question what you are asking them to do? What is service the axel? New brakes and new bearings, or just check and repack?
I paid $30 to repack bearings and check brakes when they were installing new tires a few months back. Very simple and took a few minutes. I think I have one bearing that is wearing a little, but they told me when I get tires next (5 years or so) I should change that bearing.