Glossary
Spread
The gap between best bid and best ask on that token. Round-tripping costs about that gap plus any taker fee, before the thesis moves.
The spread is the gap between the best bid and the best ask on that token. If someone will buy YES at 41¢ and someone will sell at 43¢, the spread is 2¢ — two percentage points of implied probability. Round-tripping (buy then sell, or vice versa) costs about that gap plus any taker fee, before the thesis even moves.
Tight spreads are a liquidity signal. Fifteen-minute crypto and big politics names often trade on a cent. Long-tail books can sit 8–15¢ wide, which means the “40% implied” you saw might be a 32¢ bid / 47¢ ask with no last trade in between. YES spread and NO spread are separate. A complete-set check would care about YES bid + NO bid versus $1, which is a different identity from a single-sided spread.
Makers quote the spread; takers cross it. Slippage is what happens after you finish the first level and keep going. For research, do not treat last price as executable if the spread is wide — look at the actual bid you could hit. Convert a mid into American odds with the odds converter only after you decide the mid is real.