When buying supplements why do people just buy on price?

I am curious, when buying supplements why do people buy on price and ignore the ingredient list on the back?
I have just been talking to a guy from Sheffield who said he was buying Graminex for the Rye Grass Pollen Extract content to help with his BPH and Prostatitus but it wasn't working.

I asked him to read the ingredient list on the back of the Graminex, no specific Rye Grass Pollen listed just a general Secale cereale listing. Graminex is sold as flower pollen, which he hadn't bothered to check.

My interest in this? As a Trustee of Prostate Aid CIC we sell Rye Grass Pollen Extract specifically for BPH and chronic nonbacterial prostatitis.

Our product ingedient label simply states Per Vegetable Cellulose Capsule: Rye Grass Pollen Extract 20:1: 500mg.

That's it, nothing else and he hadn't read our ingredient list either, purchasing Graminex as it was slightly cheaper, so to return to my original question when buying supplements why do people buy on price and ignore the ingredient list on the back?