Simple versus compounded
APR is the nominal annual rate without compounding. APY assumes earnings are reinvested at some frequency. At low rates the difference is small; at high rates it is large, and a protocol compounding every block produces a dramatically higher APY from the same APR.
Neither is dishonest. Comparing one protocol's APY to another's APR is.
Base rate versus incentives
A displayed rate often combines interest actually paid by borrowers with a distribution of the protocol's own token. The first is sustained by demand; the second is a marketing budget with an end date.
Token incentives also carry price risk — a rate quoted in a token that falls fifty percent was not the rate you earned.
Denomination is the biggest trap
An APY shown in dollars on a volatile asset is a conversion of a yield paid in that asset. If you supply ETH at 3% and ETH falls 20%, you have more ETH and less money. The percentage was accurate and told you nothing about your dollar outcome.
This is the single most common misreading on any yield screen, and it is why a dollar-denominated figure on a non-dollar asset deserves a second look.
Making a fair comparison
Convert everything to the same convention, separate base from incentives, note the denomination, and check whether the figure is current, trailing or projected. Then ask who pays it and whether that payer will still be there next month.
FBT Swap shows yield figures with their source and does not present any of them as guaranteed. Where a source is unavailable, it shows that rather than an estimate.