According to Robert Kirk, who recorded this information in the 1640’s a Scottish or Irish person could willfully become a seer by getting some corpse hair from a poor person in stuck to the rough sides of their cheap coffin, and then wrap it around your waist. And then observe a funeral procession from looking back at it stooped down looking between your legs.
Now this seems completely impossible. I definitely would never suggest digging up a grave! And I don’t think that is what Kirk meant anyways. I think he meant during the viewing part, where people come to pay their respects, they might have be able to get a bit of hair that got caught on the coffin and keep it. He also mentions as an alternative getting a type of ivy vine called a helix that doesn’t flower and use it wrapped around your finger.
When the sight came on you, you could see the fairies approaching you from all four directions. It could be quite frightening! But if you were prepared for it and seeking the sight intentionally it wasn’t as scary as if you just gained it spontaneously.