mkslwsk
As a climber what I see is that in general you learn your knots and practice them until you can tie them blindfolded, sometimes single handed, sometimes with gloves on!.
As a beginner you need probably two or three knots (fig. 8 for tie in, prussik for a rappel backup, double fisherman) As you progress you learn other knots for other purpose and some alternatives. (alpine butterfly, bowline, other friction hicthes, munter mule and so on) Then you stick with the ones you like most or are most versatile and you probably won't need no learn any new knot unless you start doing any new stuff (like start ice climbing if you never done that).
So, those resource are good for visual learners but once you learn it and use it regularly you'll probably never forget.
Regarding charging the client. I usually give an estimate prior to the work. If I see the estimate won't be enough I usually tell them that something isn't as expected and that I'll need manufacturer's support. If they are ok with this we keep going.
Sure they made it to promote their product and I guess there is no money involved. But in the end they show your scores and the % of all tests. If you take out the "don't know" it is near 50/50.