The challenge selling your business is that it's worth a great deal more to you because you know and understand the business than it is to an outsider.
You know what's happening so when you price the business you come up with a sum. The buyer, on the other hand, has no real idea of what's going on within the business so they have to take the risk they are taking into account. Thus their price tends to be much lower.
It's not dissimilar to selling a good but old car. You know it's reliable. The buyer doesn't. Hence you overvalue it and the buyer undervalues it.
Vin