Cards,cards and cards (and maybe GAs? ) [new GA inside ]

sell them it makes somewere around 20 cents or even more, during the end of the summersale cards go for around 10 cents or less :)
to get cards have them drop from games.. you could try trading (i dont do it but thats because iam lazy :) )

selling high buying low hardly works so dont botter, just buy and craft what you want. otherwise stay out of the market :)

I get them as drops from games, when i get a foil i sell it and buy booster packs

Or they just buy them and store for season sales to get additional card drops for free. It's a very common practise among us, level-hoarders. :D

steam and the developer / publisher get a cut of each steam community market transaction, so you won’t make much card profit that way.

i recently started using steam trade matcher to trade duplicates for other people’s duplicates and complete sets. it seems to work pretty well but it’s a bit slow going through my inventory.

steam card exchange runs a trade bot so like just now i got a magicka card pack but already have a level 5 badge, so traded all the cards to their bot for credits i may eventually be able to use to get out cards i want. the difficulty there is that their inventory is too low for cards i actually want, and if they only have 1 of a card left they charge 150% their normal credit price.

i've also bought cards at tremor games with coins earned from logging in each day and doing a couple offers, but they don't have cards for all of the games i'm interested in and sometimes you have to wait for them to approve your purchase. also right now their card trading bot which gives you the cards you bought via trade is offline so i can't get my latest purchase.

A few days back I had a bit less than 3000 cards that I was getting mostly as drops from my games since the summer sale. Now that I crafted a shitload of badges for the Mystery cards I'm down to about 1600. Besides getting them as drops from your games or random boosters it's good to know when to trade and for what. Take those 20 cent games each week with card drops for example. For those days that they're at -96% their card value drops to 0,06 -0,08 a piece for a 5-6 card set and if patient you can probably score a few on the marketplace for as low as 0.04 -0.05. Or you could trade another higher cost card for 2 of those.
Another way of expanding your card inventory is trading bundle games for cards. Pricing is all over the place and every trader has his own set of rules, some go by pure quantity, some go for specific $ value, some won't accept some cards, some will only trade if they are the ones choosing the cards etc. so there's no hard guidelines for this, just try to not overpay/overcharge :P

As for the Mystery cards there's rumours of an event of some sort during the summer sale so it's a 50-50 situation. If there's no event it's best to sell early but if there is indeed one you might want them for that or possibly we'll see an increase to their price so it could be better to save em up for now. I personally sold half of mine and kept enough to craft the badge x5 + some extras

thanks everyone , just for you a new ga: http://www.steamgifts.com/giveaway/sdjMd/company-of-heroes-complete-pack