And as you can see in the charts, only about 1/6 of the tax gap is evasion. Accounting mistakes, interpretation, crime, etc make up much more. As for Greece, it’s difficult to use as a good example as their government is not well organized and corruption on every level is far more common.
Of course it exists but evasion isn’t the first thing I’d think of when considering a cash only business.
https://assets.publishing.service.gov.uk/government/uploads/... https://www.dianeosis.org/en/2016/06/tax-evasion-in-greece/