Switch

They are both comedies where the ML is a conman. In both shows you really need to turn off your brain sometimes to accept the ridiculous situations, but they are entertaining and enjoyable to watch if you don't take them too seriously.
Also, both dramas have an amazing cast and work so well because of them. I particularly enjoyed both their villains.

Switch is about a conman realizing he's a doppelganger of a prosecutor and ending up taking his role to catch the bad guys. This drama has a break-neck pace and it's really entertaining. Sadly, while it does great with comedy, it has very weak emotional scenes. Switch has some minimal romance elements but nothing gets developed much.

My Fellow Citizens is about a conman unknowingly marrying a detective and somehow finding himself taking part in the elections to become an Assemblyman. This drama is less ridiculous than Switch, but I found it also a tiny bit more boring. It does work better in the emotional department though and provides some very moving scenes.

Same, same. Conning the bad rich people
here PMY is the lead, the way she is sleak, her dress sense as usual being superb and amazing
underrated!

The plots are very similar - two men who look almost identical get their positions switched - the criminal gets turned into a judge.

Both feature a conman character teaming up with a government worker to catch bad guys through unorthodox means.

Con artists and prosecutors fighting together for the greater good.
While Player focuses on action and swindling, Switch focuses on swindling and the prosecution.

#TWINS SWAP PLACES Trope
in both.

Switch: CtW is more Mystery/Thriller-comedy (NO romance, but leads have great chemistry)

vs
Our Unwritten Seoul is Slice of Life-ROMANCE drama.

Both dramas has doppelganger concept. The doppelganger is always asked to fill in someone important place and they do a really good job at it. also this different in aspect that there is more romance here then in switch.

They are both set in a korean prosecutor office. Both focus on crime. WYWS can be a little on the fantasy side though .

In both dramas a look alike switches places. Unlike many dramas where there is blood relationship between the people who looks alike there is none in both cases.

While Suspicious Partner is much more romance driven, I felt that the atmospheres of the two dramas are very similar. They both balanced a lighthearted feel with the action/crime side of things.
I also felt like the way the main MC's in both dramas started out kinda rocky and then they began to respect and care for each other through their line of work.

If you like the con men theme, then you might like this drama as well. A group of friends trick and con other criminals...

Lookalikes/twins who swap places as the major plotline and fun part that drives the story in both.

Rud Nee lakorn's main genre is romance, while Switch has very minimal to no romance (the leads banter cutely but goes nowhere) is more law genre.

Both are crime comedies with a chaotic group working together. Both are on the lighthearted and easy-to-watch side, with fun strategies and humour.

Both are fun crime dramas with both male and female leading characters, and an interesting squad working together. In both, the lead character solves things using unconventional methods - Jin Isoo because he’s a chaebol, and Sa Dochan because he’s a conman.

Just like switch had a lot of comedic moments in it, Psychopath diary also had moments like this.
Both dramas are actually very thrilling, the FL and the ML actually had a lot of chemistry, this may be random or surprising but the ML also had quite a chemistry with the psychopath of the story.