If some online store is getting payments from EU credit cards and sending goods to EU, then they obviously do offer services in EU. There are also some plausible options for enforceability (e.g. seizing all payments from EU), however, the major obstacle is that no regulator will care enough to try and enforce anything for a small scale foreign site. Their #1 enforcement priority is on EU businesses mishandling private data (e.g. loyalty programs of brick-and-mortar shops, telecommunications providers, lenders, etc), and #2 priority is the major online players that each affect millions of people. Most regulators still have a backlog on #1, they're just starting the first enforcement actions on #2, so any attempt for small foreign sites is years away at best.