Nepotism was a plague in my country.
Father-appoints-son was the most usual case. Father-in-law --> son-in-law, usual as well.
Still, there was this remarkable instructor in MTS who would tell us this advice: "If a co-elder suggests his relative, do not accept it! If the person has indeed the qualifications, another elder will think to suggest him". And again: "One of the worst problems in our congregations are elders' children".
Later, when I was an elder myself, I saw another kind of 'nepotism', or partiality: When an elder, or even a CO, suggested not a relative, but a close friend. There was this co-elder, 28 years old, who would every time suggest his buddy for eldership. We succeeded in holding him back for some time, but eventually he made it through. The MS in question was a good guy but was far from ready, and the sight of his close buddy craving every time to appoint him was ridiculous. Another difficult thing was when the CO was determined to appoint -or not to appoint- a certain person: no matter what we said, the CO's opinion (decision, actually) would dominate. So much for praying for guidance, and not deciding beforehand.