Problem flipping

I noticed that whenever I buy an item, I end up selling it the same day for higher. Recently started offering 1gp higher at the GE and sold it for 1gp under and still made money off the spread. However, it's not working for me anymore and I've tried using chump change to buy literally everything I can and resell but would only get consumed by the tax. Is there any way that I can make money aggressively flipping? I used to flip feathers and that's how I made most of my money but feathers are super slow pending.