When I first got into the hobby I bought a mystery pack to try it out, and didn’t really know what to buy. “Guaranteed PSA 10” was a selling point with a photo of some high end card in the listing.
The cards came and it was filled with random bulk and a PSA 10 common Larvitar in PSA 10. A card at the time that cost $1 in mint condition.
Was worth doing once to realize that mystery packs are a waste of money and you will always be better off just buying things where you know what you’re gonna get.