Gmail scans emails for receipts and collects these automatically. The purchases are neatly listed on a hard to find Purchases page on Google's My Account portal.
There you find the list of purchases that you made sorted chronologically. The listing goes back to 2015 in my case, and it includes application purchases, Google hardware purchases, and items that I bought on third-party sites like Amazon or the Lego store.
Some purchases are displayed with the correct title, others just with a number on the startpage. A click on any purchase may display detailed information such as the vendor, time and date, order IDs, items that you bought, or the delivery address.
Some purchases come without detailed information, likely when Gmail had difficulties parsing the receipt.
There is no easy way to delete information either. While you find a "remove purchase" option attached to any purchase listed on the website, activating that option reveals that you need to delete the emails to remove purchases. Apart from that, there is no option to clear all the data.
Most Gmail users may not want to delete receipts that they received in emails. It is certainly possible to backup the emails and delete them then to get rid of the purchase listing that Google maintains, but it is not comfortable either as you'd have to delete each email manually to clear the listing. Also, and that is another issue, it won't block future purchases from being listed again.
There appears to be no option to delete purchase information only but keep emails in Gmail.
Google notes that the Gmail account owner is the only one who can see the orders on the page. The company told CNBC that it does not use any information found in emails to serve advertisement.
A help page suggests that Google customers may see and delete the data at My Activity, but that does not appear to be the case. Even more problematic than that is that purchase information is still collected even if you disable any tracking feature on the My Activity website. Granted, Gmail is not even listed there under management options.
Gmail is a treasure trove for Google as email contains lots of personal information including who you communicate with and what you buy online. Since there is no way to block Google from parsing the information right now, you may want to consider using a different email account for important activity or switching to a new account entirely.
If you need to stick with Gmail, you could download all emails regularly using Pop3 and delete them from the server afterward.
Google seem intent on interfering and of course gaining more and more market share. The more they know about your choices the more they can target you.
It's all about making money and the sacrify of your privacy is not even of concern as long as their profits increase.