You're the one setting the line. Quote a payout on each event, price it fair and you survive; misprice it and the bookie pounces.
Each round shows a random chance event (dice sums, coin runs, card draws). Set your decimal payout before the bookie reveals the true probability. The fair line is one divided by the real chance. Quote too high and the bookie lays your bet; too low and it backs it, either way a misprice gives the house an edge that drains your bankroll. Survive the round with money left.
Odds Market teaches fair odds and house edge by putting you on the bookmaker's side of the bet.
Setting a decimal payout before the true probability is revealed is what a bookmaker does, and the gap between the two is the vigorish — the margin built into quoted odds.
The original inversion is that you price the bet rather than take it.
Pricing is the harder side and the one that teaches. Accepting odds only asks whether they look generous; quoting them means committing to a number that must be wrong in your favour on average, which requires actually computing the probability of a dice sum or a coin run rather than sensing it.
Odds Market is a probability-pricing game that teaches fair odds and house edge by putting you on the bookmaker's side of the table. It's an original free browser game built for PlayPendium.