Yes this is how it works, with 1 click you can place an odds that is better than others (or that only increase liquidity, depending of your settings).
As you say, it's a good idea to check that the current odds are fair. We could imagine that someone place an unfair odds with low volume, wait that you align with higher volume and take your offer to profit from a high gain expectancy. But this kind of system gaming will become harder as long as market get bigger.