A question we are sometimes asked” Are your Lists Opt-in?
Please understand that there really is no such thing as a truly valid purchased opt-in email list.  The only valid opt- in list is a list created from contacts that have opted-in to receive details of YOUR products or services.
So called “Opt in” lists sold by some other list suppliers are usually supplied on the basis that those listed have ‘opted in’ to received commercial messages via email from any party. This basically means, any message, from any sender!  But….while some of those listed might have agreed to receive email messages concerning a very specific subject, from a very specific supplier, most never agreed to receive email messages from any other third party! So if you are concerned about complaints from recipients you may find there is little difference between a compiled, web researched or so called ‘opt in’ list.
In fact,  GDPR reinforces these points in some detail.