In Nigeria civil service, it is expected that promotion is based on certain/defined criteria which should include: qualification/experience, age, years in service, promotion exam merit etc. One can't tell which criteria should come first.
However, in Nigeria in most cases "FEDERAL CHARACTER" is included. Federal character in this context is when a populous region(major ethnic group) is given higher slot or consideration undermining all other criteria for promotion.
The only recent criteria which can undermine the federal character and other promotion criteria is the "HIGHEST BIDDER". Highest bidder in this wise is the worker who has the influence to pay more in monetary terms to have his promotion. This is also very rampant during recruitment into Nigeria civil service,were you hear junior officers paying between 250k to 500k and the senior from level 8 paying 500k and above. Only God will rescue us from this menace called corruption in Nigeria.
A recent promotion released in Nigeria security and civil defense corps under the ministry of interior, is a case study. A 2014 was denied promotion but 2018 was promoted. One will ask what criterias were used or should it be that the 2014 failed giving room for the 2018 to be promoted considering the vacancies. Alas! It wasn't base on the failure but the 2018 was the highest bidder. This is one of the reasons you see some civil servants spending 10 years even more on one grade level, at the end you expect indiscipline not to be the order of the day? Like the case study don't expect the 2014 to complement(respect) the 2018. The performance efficiency will certainly be zero because of the demoralization. This issue cut across all stata of the civil service.

If you are affected in promotion with this same thing were your junior(subordinate) is promoted above you, share your experiences and ways if any of how you overcame it.