How many SEO services providers are out there as of this date is anyone's guess but when it comes to picking one, it's not really easy to pick one out of so many. Since any SEO company can write anything they wish or claim anything on their site, it is important to validate such claim before hiring an SEO company. Do a little research on Google about the SEO Company in question who you want to hire for your link building service. This way you will run into some reviews posted by previous clients based on which you can make a decision.