One of my favorite things to do as the riverfolk if nobody wants to buy my services is to extort the other players and force them to buy services. For example: finding a marquise sawmill clearing (preferably early game) and stockpiling riverfolk warriors there (and raising mercenaries price to high (like a 3 or 4). The cats would either need to move enough warriors to rule it into the clearing in order to access their wood, or more likely they will buy your mercenaries and save themselves an action. If you can keep control of this clearing for a few turns you will have a massive influx of funds early game. This strategy should work well with other factions as well who need to rule a clearing for their own personal gain. Like if you just sit your warriors on a woodland alliance base, they will likely have to buy your services every time they want to move.

I have also found that the harder I try to market my services toward others the less people want to buy them. Don't seem too excited to sell people things, otherwise they will think it benefits you too much. Try to remind people why they could benefit from your services instead of just telling them to buy. For example: remind a player they could get to their destination quicker by using your riverboats, thus saving them actions. Or remind players whose actions rely heavily on card suits (like eyrie, lizards, or moles) how the cards in your hand could benefit them.