Why on earth would someone come on MN with this story if they knew they were lying?! You'd just not post, surely?!
I'm making no judgements on whether OP did it deliberately or not, but I can answer this. It is very common for 'guilty' people to use forums and social media to try and find ways around the consequences of their actions. They have to protest their innocence to get people riled up enough to find ways to help.
We'll use OP as an example, as it's her thread.
If, theoretically, she had been shoplifting and hadn't expected to get caught, she may very well not have prepared for the consequences. Now that she's been banned from the store, her husband might find out. She doesn't want to admit to him that she's been shoplifting or banned, so she posts to find out how she can get ASDA to change their mind. These days, it's also likely that this type of thread will be picked up by ASDA, so she can use the volume of people who respond to try and force their hand.
If she'd posted, "I've been shoplifting, I've got away with it a few times but this time I've been caught and banned - how do I get them to cancel my ban so my husband doesn't find out?", she'd have got a lot fewer responses and she wouldn't be able to use the thread as any type of proof of influence.
You'll see it a lot around Primark and their strict anti-theft measures, too. The people never did it, but always want a way around the fine and ban.
I have no idea whether OP is legit or not here, and answered in that manner, but posting doesn't really suggest she is or isn't.