IMHO it really depends on a few factors:
-If you mine your own ore and have good skills in mining or use crystals
-If you reprocess your ore and have good reprocessing skills/station tax
-If you have maxed out material efficiency on your blueprint
-Where you sell
-% of corporation taxes
-% Brokers fee/tax
The first 3 obviously help with margins a ton. I always try to sell at major hubs like Amarr and Jita for good prices/faster sales.
The last two are obvious.
I usually make pretty good isk with indy, but you need to know market sell/buy prices of materials required and the items you’re selling. Always check before you manufacture and try to keep up with market trends and see what items are selling well or what items no one seems to be making or charging too little/too much for.
I’m made tons manufacturing items people simply weren’t selling since I could price as high as I wanted, sometimes at huge margins.