Seemingly unable to stop runaway tax cheating, Greek officials have taken to putting drones in the sky over the world’s most favorite island, the tourist-overrun Santorini, trying to spot evaders, including boat tour operators allegedly taking people to the famous volcano without giving receipts as required by law.

Greece’s Independent Authority for Public Revenue said a one-day operation of the drones was used to keep watch on nine tour boats, and that the violations recorded in a follow-up inspection brought in 25,000 euros ($29,400) in lost revenue.

There was no explanation why it was done late in September instead of in the middle of the summer season.

Tax authorities say they have increased inspections at holiday resorts over the summer this year but rarely without shutting down even major offenders for more than a day or two, making it more profitable to keep cheating on taxes and paying small fines while being allowed to continue operating. More than 27 million tourists visited Greece in 2017, up nearly 10 percent from the previous year, according to the Bank of Greece.

In August, during the height of the summer season, one of Mykonos’ most popular and expensive entertainment venues, Nammos, fined previously for cheating on taxes, quickly paid up 4 million euros ($4.63 million) in undeclared taxes but was allowed to keep operating anyway despite an alleged crackdown on the island.

Inspectors fanned out to check on restaurants and other establishments not giving receipts and not declaring taxes with the cheating phenomenon rolling on and fines assessed that are far less than the monies usually brought in by evading payments to the state and no reported closures.

Almost sixty officials were involved in the four-day operation codenamed Trident because of the three-pronged focus of its inspections, commonly done in the summer tourism months but failing to stop the cheating of restaurants, taverns, hotels, water sports operators, beach clubs, nightclub and tour operators who are allowed to stay in business despite repeated violations.

The operation was launched by the Independent Authority for Public Revenue (IAPR) with the assistance of the financial police and involved having inspectors auditing a business for a whole day and then comparing the takings to those of previous days, the paper said.

If large discrepancies are found, fines are imposed but some businesses then go right back to cheating because it’s profitable even if they are assessed penalties.

Inspectors were also said to be looking for tampered cash registers, where rely on software to falsify electronic records for the purpose of tax evasion but aren’t shut down even then. They are also looking for businesses who owe debts to the state who could have daily takings confiscated Trident” inspectors detected a tampered sales register in Ornos and also seized the takings at a well-known Italian restaurant in lieu of tax debts, it was reported.

The most egregious example was Nammos, located at Psaros beach who paid up the 4 million euros it owed although only last September it was found to have been a major tax cheat and only suspended but not shut down nor confiscated by the state and now has cheated again.

The club was said to sell champagne at 1,000 euros ($1190) a bottle has been suspended, reports indicated that widespread tax evasion on the island growing notorious for high living by foreign high rollers is continuing.

(Material from the Associated Press was used in this report)