It can be worth playing the market but don't expect it to replace Vana runs overnight.
You could be looking at selling something days/weeks/months after initial purchase and to effectively maximise your chances of spotting profitable bargains in the AH and the trade chat, you need quite a lot of money (several hundred k is not easy to come by if f2p). Additionally, AH fees prevent you from selling things in the AH persistently unless you're sure it would sell. If you're using trade chat, you can spend hours advertising what you want to sell.
The upside is that the markup ceiling is very high (you could be looking at a profit margin of x00% if you're really patient and/or if you find "the epic bargain").
If you have money to burn, I'd say go for it. Otherwise, the most productive thing you might do is watch and stalk the AH to improve market awareness (bid on that Snarbolax Coat Shock High that's currently at 10k, there's no hope in hell you'd win but you'll see how much it will go for when you check your bids history).
Once you figure the price of items, especially UVd items, Accessories, Furniture and Costumes, you can make money off the auction house. But frequently you need money to make money, and business is a little slow due to the small number of people who player Spiral Knights compared to other games with Auction Houses.