lol This has happened to me a few times now. I've messaged a vendor one I purchased an item as a test, instead of the cheaper one I paid for he sent me the more expensive one. I released his funds via escrow thanked him via feedback and sent him a message informing him of his mistake and told him i'd pay the extra fee as I planned to use him a ton and was really impressed.
his reply? I DONT HAVE ALL DAY TO MAKE SURE I SEND THE RIGHT THINGS IM GLAD YOUR HAPPY BUT FUCK!!!!! MY LIFE IS REALLY FUCKING HARD AND I HAVE A SOCIAL LIFE!!!!!! BUT YES PAY ME WHAT YOU OWE ME FUCK!!!!!"
lol. I then had another one just now "Hey I'm out of stock of this but I can replace with this is it ok? or you can wait till monday" both are of interest to me and equal value so I reply with "yeah thats fine if you got the stock if not im fine waiting till monday whatever is easiest for you pal!" I get the reply WHAT THE FUCK AND IF I DO IT WRONG YOU WILL GET FUCKING MAD AT ME AND LEAVE A NEGATIVE WHAT THE FUCK IS WRONG BITCH!!!" lol.
Vendor's probably as high as the ISS. Whether it's unprofessional or not is for you to decide.