If the customer comes first to you and gives you their contact then it’s no longer telemarketing IMO - at the very least not the usual definition of telemarketing which is “asshole spamming your phone to sell their snake oil”. But if you just call out of the blue, I don’t care whether what you sell is legit, it’s just not okay to waste my time - frankly the fact that your company uses these practices damages my opinion of your product already. I don’t do that to your company - don’t do it to mine.

Now I’m not sure how prevalent scams are in the B2B industry (although I would expect there are still a lot of salespeople preying on clueless people that would fall for marketing BS instead of actually evaluating the product), but in B2C, every telemarketing call I’ve received was a really bad deal at best (that a quick Google search would beat), and an outright scam at worst.