For the benefit of users on mobile devices I would be really grateful if the quoting of entire long messages is avoided. It just helps reduce the amount of scrolling needed and improves readability.
Quoting is very useful of course in many circumstances, and I'm only talking about when quoting is taken to the extreme!
If you want to thank someone, it's easier to use the mention system, so the user gets an alert from you. For the benefit of new users just type the '@' symbol, then the username and you should see a little list appear of matching names. Just click on the name you wish to mention.
We do sometimes edit posts where this has happens, but we will always mark the post as 'Edited by PJ' or similar. We never change the users words in a post without contacting the user and marking the message appropriately.
Many thanks