It's a circle of life thing, all garages loose customers for one reason or another ( you can't please everyone ) and there has to be provision in your business plan for attracting new customers. A household image like Bosch, Lucas, Bendix etc helps to demonstrate that you sell quality to customers who don't know you, that's all. Marketing. The same reason you have a website ( which is quite good actually ) or an entry in yellow Pages.
Of course word of mouth will always be the best way, reputation will never be replaced by a sign !!
Here we all are trying to loose the oily grease monkey image, trying to raise our game if you like. If you expect the public to take this on board then like any service, it has to look attractive. I believe it's an investment to be acquainted with a big name brand. Maybe I'm wrong, it's just my view :-))