This is a good little thread, and it is one I have pondered on myself. I think the main problem is that you won't get people who have bought votes successfully to admit it.
Simply because a lot of the 'good' vote buying services are bid-bots, whereby the higher you bid (and also time you bid), will determine the percentage of your vote and whether you make money on it or not.
Ergo somebody who has found a successful bid-bot strategy is hardly likely to share it.
From what I can see and have been able to glean, if you pay around $100-200 in bid-bots you can expect to get anywhere from 30-100% extra in votes, however it is by no means a guarantee.
Anybody who pays for a resteem bot, is I'm afraid throwing their money away. I have around 7,500 followers and sometimes a resteem from me is worth a few bucks, many times it is not.
Anyway, I'll resteem this and see if we can get some more people on the debate...
By the way, I'm using the nobidbot tag these days, as it has created an alternative trending page which I have a chance of getting on!
I can understand why people wouldn't want to talk about using bots from the reasons you explained but It would be nice to hear some peoples experience with buying votes or being the seller to just hear how they found the process.
Ye I also noticed that people seem to waste their money paying for a resteem because it doesn't grantee anything.
Thanks for the resteem and letting me know about the tag, hopefully I can find someone willing to talk about their experiences with buying/selling votes.