Another way earlier dodgy sites operated and exploited the value external links had in ranking results was to become a link farm
. Link farming is where the site itself has almost nothing and in some cases literally nothing in it except lots of links to other sites and these sites also contain little except more links. These links get crisscrossed back and forth and all over the place having the effect of increasing their position nearer the top of a set of results, not all of the links just connect to more links some of them actually go to a site that is selling something this is the pay off for them. All those link farm sites bolster the chance of a user reaching the few actual sites that do exist and do business sadly though by the time a user reaches the real ones all the pop-ups and linking has turned the user against them.
There are more dastardly tactics used that are being more and more effectively weeded out these days by the ever changing and evolving web spiders and crawler bots employed by search engines. It is only a simple matter of how long you will escape them till they catch on to what you are doing if you use these types of techniques. The reason I mentioned them specifically and why I have not mentioned them all is because you need to use the reasoning behind those techniques when applying SEO in a good way for your site. Except in the case of using irrelevant keywords to get your site seen no matter what the other Black Hat practices I mentioned can be used in a White Hat way.