Use free real-time odds sites to line shop. Match the same market and bet type...

https://trentonsbestthoughtss.theburnward.com/best-odds-board-layout-like-the-old-vegas-columns

Use free real-time odds sites to line shop. Match the same market and bet type at each book, then check the time stamp. Before you place it, verify the pick, price, and stake on your bet slip. Odds move, so check again right before you submit.