What sets apart black hat SEO link building service providers on the web in your opinion?

Besides PBNs, there's no secret sauce to any other black hat link building. Web 2.0 links, profile links, article submissions, etc. is something that almost anybody can do once they know the steps involved. And most of the time the content is rewritten (and not unique). So, basically, there is nothing special about most of these link building techniques and they only require time to do it. No special skills are involved. Quality of the delivered links is more or less the same unless someone has done a really pathetic job (like posting unreadable content for web 2.0 etc.).

So, how do you set apart different black hat SEO sellers besides price? If the prices of the link types they'll deliver is the same, how do you know seller A is better or worse than seller B? And would you be willing to pay a higher price to a seller if you believe the quality of the work is a little better than the others?