Could you maybe explain what you think subtlety means in this context?
Because I agree with Sabrina that it sounds a bit odd.
Moreover, I don't know how Fingerspitzengefühl garnered six agreements.
In this context, Fingerspitzengefühl would be more like tact, but it's a really horrible word to use.
In German, in this particular context, it would sound as if they were saying: Actually, you do know you need to sell these dumbos something; I mean, the more money, the better our margin. But please be a bit less obvious about it.
In particular, your text says: "...make sure clients do not feel this is the reason for the guide's interest in them..." Also, it says: "... advise them gently and kindly that they will be able to buy postcards etc. at the end of the tour." What in the world has that to do with the above?
What about
"Fähigkeit, einen verborgenen, nicht deutlich sichtbaren Sachverhalt gefühlsmäßig zu erfassen; Gefühl (3b)
Beispiele
ein feines, sicheres Gespür für etwas haben"
https://www.duden.de/rechtschreibung/GespuerBest wishes