Completely New to Touring - Advice on Buying a Van

After ruling out a static caravan we are looking at used tourers this weekend.  Neither myself nor my partner have any touring experience whatsoever.  If anyone can give us advice on what to look out for that would be helpful.  Also, It is well known when buying cars you never pay the price advertised and are always able to haggle lower - is this the same with caravans?  We will be looking at the £4500-£6500 price bracket.  Any advice welcome.