Build a parlay or round robin from live games. The fair line is the product of each leg's implied probability. Compare it to the payout your book offers to see the real edge.
Round robin
Round robins are just every combination of your legs at a chosen group size. The fair price for each combination is the product of its leg probabilities. The book pays less than that on average — how much less tells you if the bet is worth taking.
Why fair odds matter
Most parlays look generous because the payout number is big. But the fair price is usually much bigger. A two-leg parlay at +250 might look tasty until you realize each leg is priced at −110, which makes the fair payout closer to +264. The difference is the house edge, doubled.