@barberchristij
It really is important that you understand what you are buying, based on what it is they are selling.
A crowd links vendor is selling comments on forum posts. They don't own the sites, and hence can't control the moderation. Nor can they replace or change a link once it is up. At their discretion I imagine they could post a new one somewhere else for you if you had a particular problem with a link. The service I bought always gives an extra 20% links in case there is a problem with any of them.
The sites they post on are super varied in all kind of metrics. The commonalities being that they have an active forum userbase. This tends to mean that the site is big, that actually gets traffic. The DR/DA/RD/TF really aren't that important for what you are buying here.
Many on this site say that links in forum comments don't pass any link juice. Many others have found that using crowd links seems to improve SERP rankings.
My personal feel is that they do help -which is why I keep buying them-, but I additionally feel that when I add them with guest posts, niche edits, and PBNs that I can use these more powerful links with more exact anchors than I would if I didn't have a ton of other links coming in. If I get some actual traffic that is a bonus, but not really something I expect.
You absolutely do not need to buy these links, or have them as a part of your link profile, and they may not be right for your project. If you wanted you could go running around to whatever forums you like and see if you can get links to stick. That would make it free, and you can select the sites you like with the metrics you want. The thing is that it takes a ton of time, and many forums don't let you post links until you have been a member for a decent amount of time. Hence the service; for those with more money than time and expertise.
With respect to how to contact
@Stan Fox , I have always used PM on these forums. Haven't tried Skype. You'd have to ask him yourself. Go check out his thread.