Hi Cabby & Seagull,
the points you make are valid concerns, but whether you intend to keep for rental, or sell, or decide to live in it, its in everyones interest to get the rental agreement terms right (and therefore as advertised when you purchased) - so moan and complain and get it put right before signing - even if you decide to sell, having the right rental terms will make the property more attractive to buyers, as it was to us when we brought originally.
As far as buying and living in it, thats your choice, and if you want to rent it out on the open market thats your choice as well..... there is no obligation to sign up for the offered rental scheme, all you sign at first is the purchase contract - totally up to you if you sign the rental one on final purchase - however that does not mean the offered rental scheme should deviate from what was advertised - if it does then there are reasons to object.