This way you might get your answers evaluated from a real UPSC examiner.
Before getting to this, let us answer who actually corrects the UPSC mains answer sheets?
UPSC maintains strict confidentiality on who is being selected for evaluating the copies but we can hit a ball park figure of who are the "mystery men or women"- the Dhurandhars of UPSC mains..
As per 1 article, "Examiners are drawn from academia, usually experienced professors or college lecturers with expertise in the relevant subject. This means they typically have advanced degrees (PhDs) and good subject knowledge. Technical subjects might be evaluated by professors from IITs or other specialised institutes."
This adds value to the same statements coming from those who have worked closely with UPSC, pinpointing that it is the college professors who are the evaluators of UPSC Mains answer sheets.
So, as a serious UPSC aspirant, what should you do? Your top priority to get your answers corrected are your own college professors. Yes, they might not be the UPSC evaluators... but who knows...
On a serious note, professors from good institutes across the board, share almost the same academic bent of mind. For example, Econ professor of SRCC and Econ professor of Amity will share the almost the same concerns of economy in the country, will have almost the same solutions, will know the different economy curves and perhaps might be working on some paper or research project.
You might not get the exact level of UPSC Mains examiner but this will be the closest. Also, here there is a high possibility that you might be getting your practice answers corrected from a real UPSC examiner and you might not even know about it.
I do realise many of us came to UPSC field thinking "now these egoistic professors will beg me to pass their pension file and then I will show them." lol... does not happen...
For now, bridge the differences, request them with folded hands because you might just get lucky enough to see yourself achieve the dream.
What if I dont have any contact with professors? Second option is someone who cleared Mains- does not have to be an officer because they spend half the time in stress and half the time wondering whether it was worth it. So, target those who have cleared Mains and are actually good people- willing to help.. yes, we exist...
Third option is UPSC teachers and peer review- good friends who can point out the mistakes- you help each other out, honestly.
Last option is Coaching Institute. Why last? They follow the "one size fits all approach" and punish severely if you even budge an inch- killing individual creativity and uniqueness. Also they have a lot of copies to check- so getting individual attention becomes super hard.
If you have any questions, please feel free to discuss.
Good Luck!