Is it important to know anything?

I went to a gardening centre today. I wanted flowering plants for a shaded area. There were many plants in the centre, in different colours, easily overwhelming me. I didn't know which ones would grow in the shade. So I asked a woman in the garden centre's uniform for help.

She looked down at some plants in front of her, flipped a tag over, and said, "No, this one needs sun." She did that to several plants, muttering each time, "No, needs sun." She finally flipped one tag over and said, "Look, this one says, Sun to Shade."

I said, "Do you know which plants grow in the shade, or are you just checking the tags."
She said, "I'm checking the tags."
"So I could do that too."
"Right. Except most of the plants don't have tags, and some of them are wrong."

She was right about that. There was a tag buried in every ten plants or so. The plants are clustered so you can't see the tags unless you looked for them. But apparently, if I found one, I shouldn't trust it, because it could be wrong. And the woman helping me has no special knowledge of plants because she's just checking the tags, which could be wrong. My mind reels.

What's with that?