No they don't get a credit.
The reason a shop would charge a lot more than just the cgc costs is quite simple. You can submit yourself do all of the work and pay less or:
- Shop has to prepare the inventory (database for the books)
- Shop has to buy packing material
- Shop has to pack the books
- Shop has to do the cgc slips
- Shop has to ship the books/pay for insurance
- Shop has to and I can't stress this one enough answer 1000x are my books back yet, when are my books back, I can't believe my 9.8 just bought it off the rack book came back an 8.5
- Shop has to pay for return shipping which is astronomical especially in Canada
By the time you add all of that time, energy, efforts and costs in dealers are not making much on customer submissions.