Look for practical signals rather than a gut feeling: customers referring others without being asked, usage or repeat-purchase patterns holding steady or improving without heavy discounting, sales cycles shortening as the pitch gets easier to tell, and retention curves that flatten instead of decaying toward zero. If you have to work hard to convince every single customer, or retention keeps sliding no matter what you fix, spend will just amplify a leaky bucket rather than fix it.
Scaling spend before these signals are stable usually just buys an expensive, faster-moving version of the same problem — more customers churning out the bottom.