I really liked the art and the game idea, great job!!! I wasn't 100% sure what the "next sale" timer was doing but I liked how the patrons you had were directly involved in the anti-tower defense aspect of it.
The upgrades were easy to understand and reasonably priced, although I can see it getting a bit more difficult to get each upgrade at 700 gold as I wasn't getting any patrons with more than 70 gold at that point (with all 500's obtained).
I think the calculations for profit making could be refined a little or just made a little clearer, for example if you sold the basic 30 gold weapon to someone with 30 gold, you'd get a 30 gold profit, but if it was 29 instead of it being sold for 30 (and 1 loss) and you gaining 29 but losing 1 gold because of the loss, you'd just lose 29 outright. I think maybe there could be some sort of penalty (like reputation or just outright gold. or a temporary debuff for less patrons) if people get to 0 money to spend. I like the idea that the people have less money to spend because they've been spending it elsewhere instead on you (you snooze you lose!)
I like that there are different weapons and therefore classes of patrons you could have, the upgrades were fun too and gave it a lot of playability.
The music was pretty nice too, love the retro style!
I really love the concept, I hope you continue development