Valid B-1/B-2 but denied entry? Just curious

[ABN397]

This is being asked as a general question for academic interest, and not based on personal experience.
In theory, a visa does not ensure entry to the US and the person at the POE can still deny entry if he thinks something is wrong. There do seem to be instances of VWP visitors being denied entry.

However, has anyone come across a case where a person with a B-1 or B-2 visa has been denied entry? What was the reason? I can understand cases where some manipulation was done to the passport, or if there was impersonation. Any other reason?

[PraetorianXI]

Obvious immigrant intent (the POE officer suspects the person is trying to enter and stay indefinitely). Would be the #1 reason.

[peace]

People who are denied entry are people traveling on fraudulent documents,
various immigration violations in the past( past overstayers ), people stating a purpose of visit not compatible with the visa they are traveling on (eg,
entering on a B2 and saying that they have come to work) and suspected criminals (drug dealers, sex offenders, human traffickers).

ANyone suspected of a violation is taken to secondary inspection and interviewed. People who stay long on visitor visas and enter very frequently
may also be interviewed at secondary but are usually allowed in with a shorter stay.