Through TBT, definitely. Before I started trading and had just started my game, I caught beetles on the island. But now, you can easily sell holiday/event items or sets or really anything on here for a ton of bells. Or buy a ton of turnips and then find someone who has prices at 500+. Or breed hybrids and sell them for 100k a pop. Or even sell things like art or signatures for bells! etc etc
Or go to the TBT Marketplace and sell your TBT for millions, the prices are pretty crazy atm. 10mil for 100TBT at the low end.
Without this site making bells would be much more difficult.
I got a room in the museum for ores and when they go on premium (after I have the room all filled up) I feel my pockets and get around 51,000-60,000 each trip which means I get around 200,000-300,000 depending on how many gold nugget I have. Not the best way to do it, but in my bank I have about 2 mill from doing this.