The thing is that the data collected is not from the Lands Department, instead they pay researches to scrape web sites and publications for selling prices which often include agents commissions and also transfer duty. Then there are problems trusting data because some people list in Dubai today, what they want to sell on in 1 year. When the price hits their magic figure - then they know they will get a call. Lots of other reasons for differences exist, just can't think of them right now. Nonetheless, some data is better than NO data!