In the Puranas themselves it is mentioned that they were narrated by Siva to Parvati or to Visnu. It is also said that Visnu taught them to Narada or some other sage. Thus the stories told by the gods were later passed on from one sage to another sage or to a king. In the end of Puranas were narrated by Vyasa to Suta, and by Suta to the sages in Naimisaranya.
It was from a high seat offered by the sages of Naimisaranya that Suta taught the Puranas. We may gather from this the esteem in which the Puranas were held. Also that knowledge was respected more than birth. We also realise that caste was no consideration when it came to learning noble subjects. The learned man, whatever his caste, was listened to with respect.
For a general background, please see here