Video shows suspects smoothly install credit card skimmers; Here's how to protect your money (youtube.com)
You can get a skimmer for $80 on Amazon, reportedly.
They really are undetectable-looking. And easy to install.
If you suspect, wiggle the device, and try to remove it.
Or use cash. People want to create a cashless society, but man you will have nothing but problems, with government, corporations, and criminals. The end of cash is the end of freedom.