Buying at a county foreclosure or tax deed auction is where real wealth is created, but it is also where careless investors lose their shirts, and the difference between a $60,000 profit and a $100,000 nightmare comes down to one word: underwriting. With no inspection period, no seller disclosure, and no contingencies, the winning bidder owns whatever is attached to the title, which is why the foundational rule is that you are buying a position in a legal queue rather than just a house. Title position is everything: a first mortgage foreclosure generally wipes out properly served junior liens, but winning a second mortgage or HOA foreclosure can leave a large first mortgage fully intact, and tax deeds, while super-priority, may still not clear code enforcement fines, municipal utility liens, environmental liens, or IRS redemption rights. Safe title underwriting means reading the docket and lis pendens, checking for federal tax liens, and calling the building department about open permits, violations, and utility balances, while physical underwriting means reading roof lines, foundation cracks, and stripped HVAC units from the curb and setting rehab baselines by occupancy status. Occupied properties add a legal layer of writ of possession timelines, the Protecting Tenants at Foreclosure Act, and a mandatory cash-for-keys budget, and accurate valuation demands hyper-local 90-day comps rather than broad retail comparisons. The centerpiece is a complete maximum allowable bid formula, starting from conservative ARV and subtracting repairs, a 10 to 15% contingency, auction and buyer premium fees, holding costs, cost of capital, closing and disposition costs, and required profit, with an unbreakable rule never to bid a dollar over that number because the profit is made on the purchase. The playbook closes with catastrophic deal killers to screen for, landlocked parcels, environmental contamination, historic district overlays, and the FEMA 50% flood rule, along with the liquidity required to meet strict post-auction payment deadlines and the choice between a quiet title lawsuit and title certification that ultimately determines exit speed.