Buying a lot by owner and not financing, help

So the guy im buying this lot from doesn't know what to do. I have cash or check whichever if better to pay for the property. Do I need to contact a lawyer and set something up? Also, he had a buddy telling him that he would have to pay capitol gain taxes on the sale of the property if its said to be sold for X amount so he wants to say it was sold to me for a lower amount to avoid paying those taxes. I never heard of capitol gains on property, but what do I know. Any help would be appreciated.