Holiday letting regulations are now more flexible giving a choice of how rentals are licensed.
The original EOT licence still exists, where basically you declare your holiday let as a business, and declare the income on your annual tax return, but you can also deduct operating expenses and works carried out on the property. Because it is a business you might be liable to pay TEBE, the Greek equivalent of National Insurance in the UK, but your accountant can advise you on this.
The alternative method simply requires registration with the tax office and you pay a lower tax rate (previously 10% but this may increase for 2016) with no National Insurance liability, but you can't deduct any running expenses. The newer option is mainly aimed at people who let for just a few weeks each summer, rather than those who let for the majority of the season.
The rental market is increasing each year, following the popularity of self catering family holidays, and although competition is keen, nice comfortable properties in good areas are always in demand in every price bracket.