Sorry for the late comment >.< I was browsing through all my piled up notifications and saw this

Do they want an existing character? Or is it an original character?
If it's an existing character make sure you look at pictures of that SPECIFIC pony, since they have different eye shapes and stuff
Also if it's a male it might be a bit trickier
Make sure you look at male refs and not the girls as they are designed differently, the males are a bit more blocky and masculine

Since the anthro thing is mostly a fan creation, there isn't one specific way they should look
It depends on the persons preferences
They did make an official movie where the character goes into an alt dimension where everyone is humanoid. Not completely human because they are still funky colors. It's called Equestria Girls if you want to google it, the designs may help for anthro

These might be helpful even though they're on the anime side

http://fc00.deviantart.net/fs71/f/2.....21-d64v7eg.jpg
http://fc01.deviantart.net/fs70/f/2.....21-d669bsi.jpg
http://fc05.deviantart.net/fs71/f/2.....21-d62lq43.jpg

Also this person only draws porn mostly but in my opinion draws the perfect anthropomorphized ponies (as far as the proportions and head shapes etc)

http://www.furaffinity.net/full/12850211/
http://www.furaffinity.net/view/12818070/
http://www.furaffinity.net/view/10814917/
http://www.furaffinity.net/view/12778359/

Sorry Idk if that helps or not
I tried!!! Drawing something you're unfamiliar with can be really tough!!

Oh dangit... one of the links didn't post oh well

Let me know if you want any help on specific things, I feel like my reply was vague u.u

It's 2 in the morning lol >.<

Thank you! It's actually a guy w/an anthro female character & he's very...particular about how he wants them to look. I don't mind I guess, but I'm having trouble w/it since the proportions are comic book perfect female (human hands & feet) w/a pony head popped on the top. 0.o

Guhhh that is so tricky ; . ;
It's tricky when people are super picky about commissions especially when they don't have many good refs to go off of >.<