Historians of skateboard advertising may find this an interesting page. This is how things were before so much moved on line.
Rodolfo’s in Amsterdam advertised in a UK Skateboard magazine partly to reach an international market, but also (I think) to reach their domestic market at a time when there was no local magazine available on the newsstands in the Netherlands.
Mayfair Skates were primarily a roller-skate shop (although they did do skateboards as well). In the absence of a roller-skate magazine generally available in British newsagents, R.a.D made sense as one way of reaching a wider audience — even if it was not very closely targeted. (This is a bit like showing adverts for things like supplements to help your liver on this site: only a tiny number of people will be interested, but it all adds up.)
The Custom Riders advert is the one which makes the most sense and would still be there today, I hope: a skateboard (and BMX!) shop selling to skaters in Hertfordshire and the rest of Britain. The other two forms of advertising would no longer make much sense. It’s now much easier and better to do that stuff on line.