Reddit mentions of Among Thieves: A Tale of the Kin

One of the best fantasy novels I've read in the past few years that meets your criteria is Doug Hulick's Among Thieves. His second book in the series just recently came out in the US - I'm only a couple chapters in but so far it is just as good.

Also a fan of Daniel Polansky's Low Town which is hard-boiled noir fantasy.

*Links are to smile.amazon so make sure to pick a charity first if you are going to buy!

I'd say to try Douglas Hulick's Among Thieves. The main character is over-matched the entire book. He is a decent swordsmen, but he's constantly going up against masters and he's tiny, like under 5 feet tall if I remember correctly. He makes up for it by being very smart and sneaky, he has a lot of tricks up his sleeve. Also, it's just an absolutely amazing book, one of my favorites from last year.

Edit: Here's a short review I wrote about the book which expands a little on why I liked it.