<human>: Long post but worth the read...!

This story takes place at the end of 2011 when I had just finished High School. In Australia, we have a tradition called "Schoolies" where high school grads go away (mostly to the beach) and drink/party for days on end. Needless to say, lots of locals don't like the schoolies kids coming to their towns because of the noise, etc.
They ark up prices of alcohol ($94 for a slab of jack daniels, but that's another story...) 

My friends and I went to a mate's beach house and were staying there for a week. This was in a small town of maybe 1000 people. 
On the second day, I went for a walk alone along the main road, which had all the local shops. I went inside the bookshop, which looked like it hadn't seen many customers recently. Eventually found a book, it was $5.95. "Great! I'll buy it."

When I got to the counter, the guy was really chatty. In hindsight... too chatty. Trying to distract me from the transaction itself. When he handed me the eftpos machine to pay, he had his hand covering the $ amount, but I wasn't really paying attention and typed in my 4 digit PIN and completed the transaction. He gave me my book, and I asked for a receipt because he hadn't given me one. He said something about there not being any paper left, but I insisted and he went to get some from the back. Printed me a receipt, and I walked out the door. Got outside, happened to look down at the receipt... it says he charged my account $70.00 for the book!!
I race back inside and demand a refund. He sheepishly apologises ("you've gotta watch me sometimes" were his exact words) and I get my money back.

At this point, I walk out in a huff, and go on with the rest of my day..., but not before making a Facebook status along the lines of "I hope some drunk schoolies idiots piss in front of your shop during the night". 

Have a guess what my mates did that night...

Can you condense the text into three sentences or less?
<bot>: Bookstore owner tries to rip me off when I purchase a book, mates of mine unleash the glory of a night's drinking in front of his shop.