just tell you to pay for a guest post instead
Thirteen replies in and nobody has put a number on it, so here.
Ahrefs ran 515 outreach emails on one campaign: 17.55% reply rate, 5.75% conversion. They also polled 800+ people on X and LinkedIn about outreach results, and the average conversion came back at 1 to 5%. Worth noting they flag their own result as unusually strong, partly because everyone recognises the brand. If you are a nobody pitching from a nobody site, you are at the bottom of that range, not the top.
Run it at 5%. Twenty emails per landed link. Find the dead link, load the page and confirm it is still real, write something that is not obviously a template. Call it three or four hours per link, and you do not get to choose which link you win.
Now the bit I can speak to from the other side of the desk, because we sell placements and these emails land in our inbox too.
That is exactly what happens, and it is not rudeness. If a page is worth linking from, the owner already knows roughly what that link is worth. Nobody who understands their own asset gives it to a stranger because they were told about a 404.
Which leaves the thing nobody in here has said out loud. The sites that DO say yes, for free, to someone they have never heard of are mostly the sites with nothing to protect. Reply rate and link quality pull against each other. A 30% response rate on a broken link campaign is not a win, it is a warning.
Still worth doing on genuinely good resource pages. I would just want someone to tell you it is a four-hours-a-link tactic with adverse selection baked in before you build a quarter around it.