Go to most websites, people sell carlton rackets at half the rrp, which is not the same for any other brands. Why is this? Is the rrp a true representation of what it would sell for etc?

supply and demand

There's the Suggested Retail Price. And then there is the Store Price. Like Lam said, S&D. If the S was more, then it would sell closer to the SRP. :)

so a £130 carlton rrp and a £130 forza would have similar quality in build despite one being 70 and the other being 120

I think in the UK and Ireland, people are so used to paying the RRP price, whereas the rest of the world, RRP is just a value set by the suppliers or manufacturers. It is definitely a rip-off in Ireland and the UK. Carlton rackets are made in China, the production cost is much lower than the Japnese made Yonex, the bulk/supplier price is very low, so they just sell it with a large discount, most of the time.

Kind of repeating what was stated above but since Carlton produces its rackets in China cheaply, it can lower its prices as a way to entice consumers, I am not sire that it works however.