I use the rating of the SIN as a minimum rating the Verification system needs to have in order to be able to say its a fake. If so i make an opposed roll between the two, whoever gets more successes wins and, yes, Edge can be applied to the roll.
It gives freedom to characters who pay for good ID's and Licences, who can merge into the SINner society well enough, and makes the Fake SINs a very desired object. Sometimes my players go on runs just to get that shiny nice rating 5 fake ID. They are like teens all hyped-up for getting fake documents so they can buy alcohol.
In any case I deffinitely make any rating 4 fake license or SIN rare (more than the availability establishes, I simply say if there are any on the market or no, as this incetivates the use of forging their own documents), 5 is worth a lot more than the meager

5000 it is worth, and a 6 is "Panacea" for criminals.
I also downgrade -GM fiat- or upgrade Fake SINs according to use, since credit history is built, and a larger amount of data is available to cross-reference when someone checks the validity of the ID.
**Edit as two posts up doesn't state uny rule to be used... Hmm, maybe I misread or something.