Insurers have a significant incentive to get you to patronize their "preferred" collision repair shops. They keep vast amounts of money by effectively controlling repairs -- money and savings that are not passed on to you. This happens when the insurer demands a discount off of parts prices, urges the use of salvage yard parts or imitation crash parts, inhibits normal increases in rates charged for labor, and tells the repairers they cannot charge for certain normal repair activities. You still pay the same deductible you would pay at any shop. The insurer is the only one that benefits from your patronage of its "preferred" shop.
What do I say if I don't want to take the insurer's recommendation about a collision repair shop?
Be prepared: these representatives don't give up easily. Some of them are given bonuses, paid days off, or other incentives to direct you into the network. How many vehicles they manage to get into the network program is also typically an important element in their employee reviews. So they have significant personal incentive to manuever you into the network.
Some states have laws or regulations expressly defining how an insurer can discuss its "network" program with consumers. In some states, like New York, there is a statute (NY CLS Ins. § 2610) that prohibits an insurer from discussing its network with you once you have declared that you have a collision repair facility you intend to use.