I DIY now. I just looked for recipes that were similar to vendor ones. Bought the ingredients and mixed. Actually, to lower shipping costs, I only but ten flavors at a time, so I found a FEW recipes. I made the recipes, recorded heavily the notes, and put them away for steeping.
I am up to about 75 flavors for one reason or another now. Yesterday, I just happened to take my 4 Apples and added each to a bit of cream and they are now steeping. I will test each to determine the differences. Notes, notes, and more notes.
I have some tropicalish fruit flavors that I want to mix. I will prolly make about 6-7 different mixes at different percentages. Tinkering is okay.