Why the bill is bigger than people expect
Most sellers plan for capital gains tax on their profit. What surprises them is the second tax: every dollar of depreciation you've claimed over the years gets taxed at up to 25% when you sell, even if you never noticed the deduction because your tax preparer handled it. On a rental held 10+ years, depreciation recapture is often the bigger of the two taxes.
Your profit for tax purposes also isn't "sale price minus what I paid." Depreciation lowers what you have into the property on paper, which pushes your taxable profit up. That's why a property that "only" went up $150,000 can produce a $250,000 taxable gain.