I think it's fair to say that a lot of people err on the side of generosity whether it's MPG, the distance they shoot at, how deep the snow is where they live in winter or how hot the sun is in summer but there also some people who can give an accurate answer to a given question so probably best not doubt everyone at first glance.
The above members have given reasonable answers and also not over inflated the figures. Words like 'roughly' and 'between x and x' are perfectly acceptable as it gives a general guide, not an over generous 'guaranteed to do xx' figure.
MPG is subjective and it depends alot on how you drive, the maintenance of the vehicle, the tyres you use, the roads and distance you travel, the traffic conditions and even the fuel etc.
For example my Navara on 80/20 tyres is currently sat on 35.8mpg on a daily 20 mile round trip to work but it has done 61.6 for a short distance after filling up in Salisbury and following a tractor a couple of miles to Wilton.
I always use Shell or BP diesel where I can as it gives better MPG and I believe is better for the engine (less smoke). I average between 35-38mpg with this fuel yet when I stuck Esso in a couple of weeks ago I struggled to get 33mpg.
And the above figures were taken from the screen in the dashboard............