Complex sentence: The important point about solution selling is that it is essential not to sell the solution before you understand the customer's requirements; otherwise you are highly likley to unwittingly sell them on how ill-suited your solution is to meeting their requirements.
Split into simpler sentences: The important point about solution selling is that it is important not to sell the solution before you understand the customer's requirements. Otherwise you are highly likley to unwittingly sell them on how illsuited your solution is to meet their requirements.