It is probably the case that DIY processing of credit card orders is no longer allowed by the banks - years ago I ran a small business doing this, but I suspect these days you have to be 'approved' under many strict criteria before being allowed to take VISA money, etc.

This being the case, maybe the festival has no option but to use a (paid for) third party service.

That being said the figure of £12 mentioned in the first post seems far too high - just a few pounds is normal.