In your niche, if there is a directory that is good, you probably know about it. If you hire any agency that mentions directory links, you’re risking your entire business.
And Google knows full well about guest blogs, and mom blogs. In 2019, an agency talking about these techniques means you should run.
Ten thousand links from low quality sources will never be worth one good link from an editorially sound organisation like the BBC.
Google tells you what not to do to avoid getting a penalty [ Google
] that could ruin your business. If you talk to any agency that doesn’t mention them, stay away.