Hi, as you can see from my profile, I have a lot of experience with Chrome Extensions.
Implementing "snipping tool" is complicated and somehow unprecise. My approach would be to add an icon to the left of "heart" icon on each listing, and when clicked, it would be added to the excel sheet, and when you are done adding, you would just click on icon in toolbar and get excel file exported with all of the selected listings and their info.
Feel free to ask if you have any questions or doubts.
Best regards, Stefan