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There are a lot of people who claim anything they think they can argue is related to them doing work and don't realise that there are only specific things that are allowed to be claimed. Combined with people also thinking that someone in the tax office is checking and approving their returns a lot of dodgy deduction ideas get passed around on the basis that it was accepted when they claimed their tax.
Some people have potential to end up owing a lot of money back if they are ever audited. Unfortunately/fortunately (depending on your perspective) most people don't get audited so it never catches up with them. And having to pay back 7 years of dodgy claims compared to the benefit of getting away with it all the other years probably makes it worthwhile anyway.