If you have a 1000 page travel site with original content, you should be making more than 20 bucks a day. (But they don't know this. Tell them you make $100 bucks a day, and if they want to match it for a year you'll sell.)
There is such a thing as "due diligence", and anybody looking at buying a site should investigate and verify any representations made by the seller. There's also such a thing as fraud - and getting a buyer to rely upon figures that you cannot later prove to be true, in order to make a sale, could create a headache you don't want.