I know how most link builders work!
They just trade lists and resell guest posts on blogs created just for this purpose!
Then after you check their 10.000+ blogs list you find out that only 10-20 blogs worth using for your guest posts
So I did all the hard work for you and I build relations with real blogger that not only have good metrics but they also have readers , get social interactions , comments etc.
Check this spreadsheet to get an idea about the metrics and prices and if you are interested p.m me or reply here for more details.