Personally, I like to deal with the dealer when I can. They have proper tools and training and are only fixing one make of car. But, it's best to know where you stand.
Get a second opinion from a shop that's familiar with Volvos. Have them explain what they're proposing to do, what parts they want to change, where the parts are from and how much it will all cost.
It usually pays to compare.
I have an example recently from my Jeep GC. It was time for my 100,000km 4x4 service so I checked with my usual dealer and then another Chrysler shop in town. Dealer #1 $650.00, dealer #2 $450.00. I went back to my usual shop, asked the service manager 'what's up' and he explained the difference. The second shop advertised, as part of the service, "transmission pan drop, filter change and fluid". Shop #1 says that that's only the simple part of the job. The proper service includes transmission flush which is a more involved process and requires 13 liters of ATF, hench the price difference. I went with dealer #1.