I don't doubt for a moment this happens, but they can lose their ability to procure vaccines in the future if their practice is identified.
Sometimes it occurs due to lack of understanding, poor training, or poor oversight. But no vaccine--especially those under emergency approval--should be administered outside the ACIP-CDC guidelines. The Pfizer was approved for the 3rd dose you sought. Moderna was not. And this is especially an issue given it appears that even Moderna wants the 3rd dose to be a HALF dose based on its own data and to avoid any increase in adverse reactions. My guess is you received the full dose. since that would not have been known to them
Serious issues can occur when providers do this kind of thing. This clinic learned the hard way (and they are not the only one):
Colorado health department pauses COVID-19 vaccinations at Colorado Springs site
CDPHE said it halted a vaccination effort after an inspection revealed the clinic had failed to comply with storage protocols.
https://www.9news.com/article/news/health/coronavirus/vaccine/colorado-health-department-pauses-covid-19-vaccination-el-paso-county-site/73-2997c613-c7a0-4e3f-ad62-1eebc5ff40e3
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