basicaly, you ned to install python and run this app in command prompt/console.
to run it you need to install python(its free, google it, common tool, if you are on linux/mac most likely you already have it)
then go to directory where the file want_needs_working.py is in console/command prompt.
type in: python want_needs3.py
???????
Profit!
first time you run it - it will ask for URL of your steam offers page https://www.steamtrades.com/ then it will ask you for second URL of person who you want to trade with.
first time you insert ypurs - you dont need to insert it again. just hit enter when it akss you for your URL. it is already remembered.
once app finished - you will know which games he has - you want. You will know which games you have - he wants. if any.
Little bonus. if you tun app with: python appname l
it will try to see if other guy has games on Linux. and tell you which one he has on actual linux. It will give a few false positives very likely. Just look at URL vs name of game.
If any mac user ever comes across this tool - let me know, ill modify script for mac, its simple.