When I was younger, decades ago, I always wondered why investors keep saying we need to have customers and revenue first before plonking down millions; why would I need investors when I have paying customers?? Then we got paying customers, customers paying millions/year and we found out why we need investors. Not all businesses do but even little more than slow growth is pretty hard when bootstrapped; we exhausted bank loans pretty fast as they are too conservative.
if marketing / sales is free you can scale it up without funds. unfortunately, i came to experience first hand it is not. i doubt you can scale without paying for marketing somehow.
I have found that the more excited that a customer is excited about a product the more apt they are to be your best salesperson. This was especially true for
one of my consumer SaaS.