I just started playing the game a couple days ago but my second game was with the inn and i got to the master lvl with it and made a ton of money. I found that if i had beer and food in my shop inventory before i went to bed or whatever then there was a (I think it might be random) chance that it would say upon waking up that my customers enjoyed my inn and i would get money.
So i would sell all my beer and potions first thing in the morning and then stock back up on them durning the day so that i could get paid money (randomly) at night. The amount of money i would get seemed to vary wildly too. I did find that i think around the fith lvl of inn job progression i could build a regulars table and i would randomly get tones of money from that. The money i got from the customers seemed to be in the hundereds most of the time and the money i got from the regulars was usually in the thousands.
If anyone else has any other suggestions id like to hear them too but thats what i gathered from playing inn keeper for a couple of hours.
Reinmar: There are also different bonus sources of money you gain by buying relevant upgrades: dark corner, where you can send out spies, and people will buy information they get (unfortunately they don't go out automatically and you have to click every time) and regulars table which gives you a solid chunk of cash every year for no effort. But those upgrades require higher level of building from what I remember.
Holy crap you can get money from the dark corner. I didnt know what it did so i didnt mess with it too much. Is it alot? Is it based off your stealth skill? Also i agree on the skullfire that thing would sell for a whole lot. Also do the customers only drink weak beer because once i reach master lvl i completely stopped producing it and only made expensive beer and potions and made sure i had around 15 meals in stock that i never sold at the market.