Is there information about the buyer and seller in the Blockchain? Suppose I wanted to track transactions by an individual entity in the Blockchain, say Mr. Smith. Is that possible?
Yes &amp; No

You can track a person's transaction only if you know that person's wallet address/es

By the wallet address/es, you can see the transaction.

The incoming transaction can be a buy, or a sale completed, etc.

The outgoing transaction can be a sell, or a purchase, etc.

You can also track a person using all his xpub key to know all the address/es at once.

Buy you cannot track a person just with a name or a single wallet address (if he owns multiple, which at this time, people do).

Hope this answers your question.