Welcome to CC Bratt!
Yes you asked a hot topic question...but eventhough I have answered this on several other threads, I will answer you as well. I'm in a good mood today.
I use both mixes and few (very few) scratch recipes. Most of the mixes are doctored, but there are a couple that are straight. I only use DH, have tried the others and they suck, especially Betty Crocker, Pills is an ok second to DH, but it doesn't yield as much batter so in the long run is more costly to use.
My icings on the otherhand are 100% from scratch. I use a equal salted butter to Hi ratio Shortening with stable pasturized meringue, less p sugar than most buttercreams, and add pure vanilla, cornstarch, and a bit of Cream cheese to make the butter flavor "POP", my BC does not crust, I personally don't like the taste or texture of crusting BC's and obviously neither do my clients because my BC icing is what they always rave about. There isn't a set recipe with the dry ingredients as the amount of sugar & cornstarch depends on how humid or hot it is (I'm in Texas). So basically made to taste & texture. I pretty much have it down to a science though.
My ganache is premium chocolate with heavy cream and butter. Royal is pasturized egg whites (not whipped), with p sugar and lemon juice. My Cream Cheese icing is the same as my BC, but I use 80 oz of whipped cream cheese so never the cream cheese icing that others seem to have. Those are the only icings I ever use.
I do order my fondant from Fondarific, and won't use any other brand now, and I have tried them ALL, even the homemade. The homemade is just too time consuming, and it is another bowl and beater I have to clean...not interested.
As for my clients...I have never had a client ask me if my cakes are from a mix or scratch. But if they did I would be honest about it. The reason they don't ask is because they taste how yummy and moist my cakes are, and how my icings don't overpower the flavor of the cake, and they don't really care how I acheived that level of excellence in the flavor of my cakes, they just love them.
I worked at 2 different custom bakeries in the past, and both bought and used straight from the box with NO doctoring Betty Crocker mixes because it is the cheapest; the used the gross shortening only BC (still wondering how someone can call it buttercream if you don't use any butter in it). Did they ever tell anyone their product was from a box?...nope. And they were still churning out 200+ cakes a week. These were NOT grocery store bakeries. That is a WHOLE other issue...LOL!