There are organizations called blacklists like Spamhaus as well as other filtering organizations like Cloudmark and Brightmail. Email clients like Yahoo and Gmail and Hotmail rely on them to help block spam (yay!). These blacklists leave spam traps or honeypots for shady list sellers to collect. Then, if one of those email addresses ends up in your purchased list, you're in big trouble! It's like having bad credit - it can take a long time and a lot of hard work to rebuild trust with blacklists and until you do, you'll have poor delivery results even if you've stopped using the purchased email list.
InfusionSoft is a fully functional CRM and marketing solution created for small and medium size businesses. Comparing it to MailChimp or AWeber is like comparing a Lamborghini to a VW Golf. It provides highly advanced features for list segmentation, lead scoring and marketing automation. On top of all that, you can integrate all of these features with your optin form using Infusionsoft Tags + OptinMonster.