keep in mind a rwc is a legal document, and if you sign it you assume all responsibility for it. and a person who begs for a favour or 50, will also very happily sell you down the river to the cops without a care: "but i just got it road worthied by xxxx".
i used to do rwc when i worked at a dealership, and the amount of pissing and moaning and abuse over all sorts of things turned me into a real nazi on principle. so if they're hard on you it's most likely because of the last 100 bitching, lying arseholes they had to deal with. one bloke told me, as i was about to ride his bike "the speedo's not working, but don't worry about that, it'll be ok" and then screamed abuse at me when i failed him for that and various other things.
if you turn up with a bike that's clearly not roadworthy, then you can't expect to get one. make sure you know what you're going to be tested on, and prepare. i'd always say start with an original bike, get it done then start playing. proving you can do it is a complete waste of time, as you seem to have found out. all it's doing is costing you money and time and agro, it's not worth the effort if you can avoid it. if it's not going to pass, it's not going to pass. if it's something you've spent a lot of time on and that's obvious then the person failing you will probably apologise for having to do so, but that's the way it is. remember they didn't make the laws, but you made your bike the way it is.
i'm very happy to not be involved with them. and since i stopped doing them they've been made tougher, with photos required, etc.