Hi Get A Grip. I notice on your website that you aren't a registered charity, rather that you have a company number and are registered as a Private Limited Company at Companies House. Due to this, even if it is for a good cause, you are required to meet the same set of requirements as any other poster on the forum. That is that you must fulfill 50 posts before you are able to sell on the Forum.
It also brings in to question where £5 of the £6 that your grips cost is actually going.
I would suggest that unless the likes of Arytek or Aedos (who happen to be featured on the getagripuk.org.uk site) are able to coroborate your background, I would suggest that forum members are wary of parting with their cash.
I'd also note that while using a .org.uk extension on a website is not a crime, these domains are supposed to be used by charities and it does suggest a level of insouciance.