You can check the len against the light (the side which is mounted on the camera body). Just put your len against light, tilt it slightly to see the clarity of your len.
A distinctive fungal infected len have a cystal-like lines/flake forming around the len especially at the edge of the glass. A good/clean len should be free from any of these lines. They are clear just like cystal.
erm how about tinting? last time I idiot went to clean lens at shriro for $200, but in the end the lens was tinted yellowgreen...
the shops usually have a trial period with money back wty or exchange?
I won't know this. I never had any problem with my len yet. (keeping my fingers crossed.) Maintain your len regularly. Even if you are not using, make sure you take them out once every few months to clean with blower and check for fungus. After which keep them in the drybox. After every shoot do not keep your len immediately in the drybox. Let it rest for a few hours or a day, clean the len and exterior with a good blower and a clean piece of silk before keeping them into the drybox.
As for servicing in camera shop, I don't have any experience regarding this. Anyone care to share your expertise?