Are you buying a Landscaping biz (design & install), or are you buying a maintenance company???
If it is a landscape operation, you need to consider whether or not you are qualified to operate it. If you are buying a one man operation then all you are really buying is the soon to be previous owner's reputation.
The previous owner's reputation is of no value to you unless you hire him.
If you have landscape knowledge to begin with, then just start your own. It doesn't take a huge investment to get started.