Hm, currently, if I have never played someone, and I want to know what their relative skill is there are a few things I check in their profile.
Firstly, the date they joined, people that have joined earlier are typically more seasoned, and more importantly, as well as knowing all the ropes and bugs, they know more people than you do, and may have prior relationships.
Secondly, check their win PERCENTAGE. Don't just look at the wins as a lump sum, because that just may be indicative of someone who handles a lot of games at once, which may increase their experience, but lower their quality of individual gameplay. Count all their finished games, and find a percentage. Of course the percentage is all relative, but compare it to your win percentage. Most of the veterans have at least 20% win/total, I believe.
Thirdly, check how they are doing in their active games, especially their later active games, as opposed to one that just started. Check their unit count, that's the best indicator of their prowess, although it does not always mean they are skilled.
Fourthly, you can check what countries they seem to excel with, and which they have trouble pulling off a victory. It helps you watch out for them in new games.
Lastly, in-game, send them a message. Ask them questions, about what they think about other countries, about what they plan to do, about which countries they favor. Whether they answer or not, how they answer, and how their answer corresponds with what you've heard from other players and how the pieces are placed on the board can tell you a lot about a player, as well as help you gather some intelligence.
So, those tips are good indicators of another player's skill, although none of them are entirely accurate. Personally, I pride myself on playing only a few games at a time, but maintaining a very high win percentage. I am currently at a 46.67% win percentage, which is the highest I've seen so far, out of people who have played more than seven games. Most people just look at my seven wins and assume I might be a rookie, very few check my total games as well as the time I joined. Remember to respect all players, regardless of what your intelligence brings up.