I can only state my personal experience.
I spent all of classic vanilla building my reputation on my realm. Helping people level, giving free dmt buffs to tanks and healers, I even got recruited for a few weeks on the top guild on my realm for a little while, but I left after being benched for a month straight. They likely invited me because I gave dmt free to any guild member, and if I was selling to them instead of free I likely would have made an extra 2-3k gold from that month I was with them. I left that guild after finding out they were using me for free dmt.