This is such good advice.

I think new founders are sometimes intimidated by customers, especially well-known brands, we don't want to upset or annoy them instead of being open about not being able to afford to run loads of pre-sales technical work. We also see the dollar signs for one large customer when we should be seeing smaller dollar signs for many customers.

For the customers, to be fair, they are partly trying to derisk the purchasing decision by making sure everyone and their dog has seen the demo, shown that it definitely does exactly what they want with their data and processes etc. and they have no skin in the game at this point, so why not?

Believe in the product you have built already and as the OP says, be certain of product market fit and ABC (always be closing).