yup it’s a rip off but if everyone did this sort of thing then i’d be out of work fixing computers 
VW used to make it a requirement of their warranty that cars had to be serviced by an authorised service agent. As a result they were taken to court and were fined billions of pounds.
The reason is that under the Treaty of Rome, customers only have to show that the vehicle has been serviced by someone competent using genuine parts rather thanan approved agent and the warranty must be honoured. This also applies to imported vehicles within the EU.
Hence the reason why Honda now state in their owners handbook that they “Recommend” that bikes are serviced by a Honda dealer, they do not insist on it.
A competent individual can include someone working from home or a non franchised dealer, so providing it is serviced within the manufacturers specifications, they cannot refuse to honour the warranty.
Do it yourself…
Download a manual from scribd.com (sorry I haven’t read your thread so don’t know what bike you have but you should find a manual here).
Buy new spark plugs off ebay.
Buy a new oil and oil filter bumper pack off ebay.
Buy some coolant and Dot 4 brake fluid off ebay or Halfrauds.
Read the manual you download (concentrating on the areas for service).
Take a weekend out of your time.
Fit replace / parts.
Save money (and ensure no robdog dealer is saying one thing and doing another (like not bothering to change your sparks cos they’re difficult to reach).
Simples!
Learning how to work on your ride not only saves you money, it ensures the jobs are done as unfortunately more and more workshops are betraying the trust a paying customer should be able to have in them.
If you are time poor, money less poor or rich however…Take it to Southern Cross Motorcycles in Kilburn (do a search) 