Rather than a fee for my services, I base the fee on replacement costs and difficulty to replace.
For example, often, the price to replace a 4x10 foot impact (hurricane) window is well over 300 bucks....even much more...my fee is going to be 300 bucks.
Shower enclosures will be the same price as replacement. here is why; replacement is a much bigger hassle...not to mention that often, stuff gets torn up doing the replacement!
Then again, a 6 inch scratch might only cost you 55 bucks to repair...depending on depth...length etc.
Water spot/stained windows are the easiest to fix but require the most concentration...simply because it has to be perfect...or no fee.