Ask HN: How do you get honest feedback on your side projects?

Ask people to pay for it ...

I saw http://www.ideacheck.io the other day, so maybe that can help (I haven't used the service myself).

Recently read somewhere, instead of "feedback", ask for "advice", who does not like to give advice? :)

Ask potential customers to pay for it and they will often give feedback.

Ask questions in the negative, such as: "What don't you like about it?"

I have tried friends and family but it doesn't work. They are holding back on their criticism.

why not show HN?

Yeah, "Show HN" is definitely one possibility. But personally didn't have much luck there, so looking for alternatives.