Ask HN: What was your experience consulting a PR agency for your campaign?

I have two cases working with PR agencies, one for a product that already had many users. We wanted to promote the product in different sectors by attracting media. Second, we wanted to run a crowdfunding campaign so we hired a PR agency to build the community before the campaign and attract media during it.

Both cases ended up complete failure regarding the performance of agencies, despite the product and the campaign went very well with our own efforts.

To understand why, I'm trying to know about others' experiences working with PR agencies.