"this is not a sexual service"
is a disclaimer that most, but not all, adverts contain because Gumtree rules are:-
"Ad that contains adult, mature or erotic content are not allowed."
This means if they advertised HE, B2B etc then their adverts would be removed immediately.
Most people here understand that.
So when looking at Gumtree ads you need to "read between the lines".
Ringing/texting them with questions about "extras" will frequently get the same denials ... they need to be cautious because you could be a Gumtree representative checking up on them. Similarly, don't go in a shop and ask at Reception ... anybody could be listening.