You didn;t specifiy that you were going to do this thought it was more a gneral 'can this be done' type question else I'd written this up earlier for you;

Proper accimlimation should follow something like this for dramtaic changes in SG

- check the SG of thier current environment (LFS or wherever) preferably with a rerefractomoter
- setup another hospital/quarentine tank with water mixed to the same SG.
- use the standard drip method accimate your new fish to their new (temp home) a hour or so will normally be find
- slowly raise the SG, daily pull 10% of the water volume out and replace it with your normal salinity water (1.025ish)
- continue this until you reach your normal SG in the display tank, this should take several days at a minimum.

- now coninue to observe the critters in the QT for a few weeks, just as you should quarentine any new arrival.

- after 4-5 weeks if all goes well, drip acclimate the fish to your display to the display tank. again another hour or so, and they should be okay.

This is the method I used for my snowflake moray eels that were being housed in 1.018 water at the LFS.

A decent LFS won't mind you testing their water and stuff before making purchases. Though you'll likely encounter more than a few jerks out there, if so then consider wether they deserve your patronage and hard earned $$$. Sounds like you really got the shaft.