Purchased email lists
A purchased mailing or contact list is a compilation of email addresses obtained from someone else, such as an email broker. Businesses often consider buying lists so they can gain easy access to specific email addresses. Consent is non-transferable, so using purchased lists is illegal and not a legitimate marketing strategy. The CAN-SPAM specifically states that it is illegal to sell or purchase email addresses. Basically, steer clear of these lists.
Rented email lists
Typically, rented lists are used to send a one-time email campaign to reach a new audience quickly. The marketing manager does not get to see the list itself when renting it. This will result in the marketing manager being at the mercy of the list holder with respect to the validity of the list (consent) and the sending of the campaign. However, even if the email is sent by someone else, if the content is yours, you are responsible for it.
The dangers of using these lists
Subscribers on a purchased or rented list did not explicitly consent to receiving emails from you. Your emails will likely be marked as spam, and your business relationship with them will be tarnished even before it begins. The use of these lists will also affect the delivery of your email campaigns as a whole, thereby affecting the people who have consented to receive your emails.
Members on these lists may feel that you are using bad marketing practices and flag your campaign as spam. Specifically, this practice could, therefore, result in bounces and/or a high rate of complaints, thereby tarnishing your reputation as well as that of the list holder.