To start, the big problem with Small Favor is the lack of bold text, playing this provokes an attack of opportunity. Then there's the fact that it won't hurt elites. These points combined makes the card near-unplayable solo.
So, the unique abilities.
Dealing 1 damage to an enemy can be done with regular fight actions. This card allows you to secure a 1 damage hit (for 1 action, 1 card, 2 resources), but unless you've spent another action to evade then you're gonna get punched. The usefulness of this shoots up when you need to guarantee a hit on something but the non-elite rule might get in your way in a big way in these cases. Slightly better in multiplayer.
2 damage is much more impressive, still the opportunity attack issue persists. Most of the time you play this like an over costed Sneak Attack. The vast majority of characters will prefer using this money for a weapon.
The range potential is the saving grace for this card, and even then it's undercut by the non-elite moniker. The actions saved by sniping a 2hp enemy 2 locations away can be tremendous. Great for enemies who behave like an Acolyte or Whippoorwill.
The best case scenario for Small Favor is a multiplayer game in scenarios where enemies tend to spawn at a distance, you play it to kill or finish enemies who spawn around your buddies or enemies who play hard-to-get. This card is very expensive for what it does, 2 damage is something you do in one action with just about any common weapon, sure the range aspect is nice but you really pay through the nose here.
All in all, A weapon will probably serve you better than Small Favor.
I cannot help but think that Small Favor should have broken ranks and had different costs or even dealt a maximum of 3 damage somehow. The other service cards are both pretty useful for their ability to give you a "double success", evading 2 enemies in one action is a useful rarity and discovering 2 clues in one action is desirable in any class, dealing 2 damage in one action is something every single class can muster with ease (except ), this means that the 1-2 damage you deal for 2-6 resources is just incredibly inefficient.
Obviously, 2-6 resources are no big deal to Preston Fairmont, I'll struggle to justify it for anyone else.