I don't really do sales and we live in a rural place so it is difficult to do the actual shops but last year I was going to have a look at a specific shop for something for one of the dc desperately wanted for their January birthday which was in store but not online .
A relative who used to work for this store and goes to the sales every single year said to me that I would be better to wait till the 28th (the shop isn't open boxing day but is the 27th) as this particular store didn't reduce everything straight away on the 27th or get all the rest of their old stock out. Due to her job I thought she knew what she was talking about.
I did wait and when I went everything was gone. She then rang me for a chat and told me how she had gone on the day she had told me not to go and bought the one item she knew I had wanted for the dc and nothing else, I must point out at this point that when dc had mentioned it relative had never even heard of the brand and still cannot pronounce the name. She then gave my dm the contents of the item as she only wanted the tote bag it came in. I was a bit 
but obviously she can buy what she wants.
Come boxing day this year I thought I would have a look at the sales. As we were over at a joint relatives house and the same relative was also there she asked if she could come too. I agreed because saying no would have made me look a twat. Her husband offered to give us a lift there which I was grateful for rather than us walking.
We get down to the shops and her husband offers to pick us up when we are done. Fab. We had been in the shops for around ten minutes when she told me her hubby was going to pick us up on the way back from dropping a present off at another relatives. In five minutes.... She then spent the next five minutes making a fuss about looking for her dh car and making sure she didn't miss the car as he was coming to the drop off point so literally I had ten minutes to look in one shop.
I said I would walk back when I was ready and was told that she had told joint relative that we were on our way back and so joint relative had already started cooking our meal. Her husband turned up and said he would have come back out later for us so we had time and she told him that they hadn't started reducing everything yet which wasn't even true and I did say so ...
She has just rang me this morning from the sales to tell me all about all the items she has bought in her full morning shopping at the sales and I am a bit wtf about it.
Aibu to think she has now sabotaged me TWICE on Christmas sales so that she can make sure I didn't get anything she might want to the point she sought out something from a shop she had never heard of!