If you do proper customer development with your MVP prior to product market fit, then by the time you hit PMF you will already have your reference customers - your 'social proof'.

Regarding the statement that SF is the ideal place to find early adopters...

Maybe that is more true for b2c than b2b early adopters, because - and here is my question - isn't the place flooded with founders trying to canvas people/companies to try their product?