It is large industry. More than one of my acquaintances got their green card and then citizenship by paying $20-$30k for fake marriage to a US citizen.
Greece has a program where you invest 250k euros (real estate is a common one) and you get a residency permit good for 5 years and can be renewed as long as you still own that real estate. After 5 years you can apply for a permanent residency, five years of that you can apply for citizenship. Now, Greece isn't the best country but even as a resident you and your family get total access to the rest of the EU.
https://www.goldenvisas.com/citizenship-by-investment-greece
> Because of the need to reside in the country the Greek golden visa program is considered a residency investment program rather than citizenship by investment. However the option for citizenship is there for those committed to living in Greece.