As I always mention, try to close a deal as fast as possible because once their appetite of buying is drying up, you will lose the deal.

However qualifying customer is the most basic and the very first step we should filter before engaging into a battle.

You need to check the amount of desire or passion to purchase the product before putting in the amount of effort to persuade.

After you notice the customer is looking or asking about the product, give a breif explanation on the product and services within 3 sentences.

Then you should ask them whether they could purchase it by making their own decision.

When they can buy it?
Can they afford it or bring money out?
Whether are they alone?

All these information will help you determine whether you can close the deal. This method is important so that the salesman could focus on each deal and adjust their salesmanship accordingly.

For more methods, you may drop a comment to discuss further.