I'd first check if those "bridge sites" are really black hat or simply a very labour-intensive and effective way for them to increase their SEO efforts. What's the quality of those sites like?
Also, sometimes sites have a short-lived improvement on Google by using black hat tactics. However, sooner or later Google catches up and penalizes them. So be careful about copying them!
Also, sometimes sites have a short-lived improvement on Google by using black hat tactics. However, sooner or later Google catches up and penalizes them. So be careful about copying them!