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Most resellers underestimate their costs. Platform fees stack — eBay charges differently by category, Poshmark flips from a flat fee to 20% at $15, and promoted listings add another layer on top. One wrong assumption turns a profitable flip into a wash.
ROI tells you more than profit ever can. A $20 profit sounds good until you realise you had $200 tied up for 60 days. ROI and annualised return show you which flips are actually worth doing — and which sourcing channels deserve your time and capital.
Tax surprises destroy resale businesses. Self-employment tax alone is 15.3% on top of income tax. Resellers who don't track and set aside money quarterly often owe more than they have — and can't pay it. Know your number before April, not during it.