Morning. Honestly it's a good question, I thought about it. I've added the websites as a source of information. If there is no website, then based on the social media (Facebook and Instagram). And if there is nothing, then yes, Google Maps. 
1. Google Maps: I've checked, it seems, you are right, I'll try to find another source and delete the link to Google Maps. It's easy to identify all such changes. 
2. Facebook: I read a couple of discussions on this issue like this https://community.openstreetmap.org/t/use-facebook-instagram-business-page-account-in-addition-to-add-a-poi/106036/2. I haven't found any clear answer. However, I believe that it's okay to treat official accounts of the businesses in Instagram and Facebook, as their website. If you saw any other information, please point me out. 
Thank you for your comment, it's really helpful! I'd like to add the initial data based on the online sources and then visit these places to verify information. 