Question

One of the important things a salesperson needs to determine while qualifying a prospect is:

Answer 1

One of the most important things a salesperson needs to determine while qualifying a prospect is if the product fits the needs of the consumer. 
Does the prospect need what your selling? Is there value? Can the prospect use what your selling? Is it worth your (the salespersons) time?

Answer 2

One of the important things a salesperson needs to determine while qualifying a prospects is whether the prospect really needs the product or not?

Salesperson needs to find out customers who needs the product. The product of the company must fulfill the customer's needs. If a salesperson finds out the customer's needs, he will be better able to deliver him the right product that his company offers. Basically targeting the right customer for your product is the key.