When someone is truly serious about purchasing from you, they will be willing to say so and sign an agreement. If they hesitate or refuse to sign, you've missed something. In this example, the person who gave a verbal 'yes' two weeks ago is not responding today. Ask for the order. Ask why another company might win the business. Understand where you really stand.
Thinking that being asked to submit a quote was proof of real interest.
The only interest may be a need to justify their current supplier, pricing, etc. A Request For Quote is simply an invitation. In this example, the seller is now playing chase with purchasing. Know if there's an incumbent, who the stakeholders are, the process they'll use to make the decision, how they plan to communicate with you. Understand the time and resources you'll need to prepare the quote. Do you really have a shot at the business? If not, what's your rationale for quoting?
A prospect was quite interested and, therefore, likely to purchase
Someone who is genuinely interested in learning more about your products may never purchase. In this example, the opportunity was noted as 90% likely to close. Yet the seller didn't know what was needed to get them to 100%. Nor did they know when a decision would be made. Reality: 90% likely to remain in limbo.
Remind your team that failed attempts are not failures. Encourage your sellers to keep trying and teach them how to tweak their techniques. They'll soon be reminded of all they've learned and how even small failures fueled their success.