You can check the axle alignment with a measuring tape. It's likely the way the shop will do it.
Measure from a fixed point on the tongue Like the leading edge of the hitch at the ball in the center, back at an angle to another fixed place on the first axle outboard near the wheel. Note the distance to the nearest sixteenth of an inch or less if possible. Repeat for each side of each axle and compare the distance. If they vary on any axle by more than a sixteenth it is out of alignment.
Now some axles can be aligned fairly easily but I am not familiar with your trailer.
While you may not be able to fix it your self this will tell you if alignment is the real problem.
As for shops there are many in the Seattle area. Try the big trailer dealers like Fruehauf, Dane etc but they are usually backed up with big trailers.
The phone book under TRUCK Alignment or TRAILER alignment will list the big shops. A web search will get you mostly Yelp and Yellowpages results that are not what you are really looking for.
