al-Qalyuubi defines al-muruu'a as: A characteristic which prevents the person who has it from perpetration of despicable behavior.
Rulings related to al-maruu'a
According to Shaafi'i [and Maaliki] fiqh if you are a sweeper then your testimony cannot be accepted because the job of sweeping undermines al-muruu'a.
Kuwaiti Encyclopedia of Fiqh Page 35 Volume 37
In addition to avoiding major sins and not persisting in minor sins, al-muruu'a is a condition in the acceptance of testimony. [Kuwaiti Encyclopedia of Fiqh Page 34 Volume 37]
I honestly wonder how many person's testimonies would be accepted in today's era? And I wonder how many cases are concluded based on testimonies of people who were never worthy of having their testimony accepted.
Eating in the marketplace undermines al-muruu'a, and hence your testimony is to be rejected [of course this was in the books of Fiqh when such an act was looked to be evil whereas now it is not].
So, either your testimony is rejected for eating in the marketplace or we have "evolved" to accept an act which was otherwise looked to undermine al-muruu'a in the past. How interesting.