I'd be wary of investing time, money, and/or effort in someone who was only willing to get certified if it was free. Once they're certified, are they going to pay ~$50 to rent gear every time you dive together? Or are they going to spend upwards of $1000 to buy their own? Are they going to pay ~$150 a day for boat dives, and then give the crew a decent tip? Are they going to spend thousands, perhaps tens of thousands, on vacations to dive destinations (and then spend their time there diving instead of doing something cheaper, easier, newer to them, more conducive to selfies, etc.?)
I offered to pay for my friend's OW course in hopes she'd become my dive buddy, because I knew she was saving up for her wedding and making a lot less money than I was. She declined, but still took the course with me. That was two years ago and she hasn't dived since. Probably a good thing she didn't take me up on my offer. If you're considering teaching your friends, in addition to the other concerns raised, you have to ask yourself how you're going to feel if, after all that work, they never end up diving again.