Implied volatility derived using standard models isn't the same neither for every strike of a particular maturity. nor for different maturities.

Volatility Arbitrage, sometimes called Volatility Bets, is a alternative way to manage money using markets and derivatives.

Ratio Spreads enable to be wrong on an asset direction.

There is no vega in the Black & Scholes model. Implied Volatility is taken as a constant. Traders modified the rules.

Barrier options are almost exclusively OTC (Over The Counter ) products. Replication with vanilla options is sometimes a better deal.

Binomial Tree Excel - Numerical model are sometimes really easy to program using VBA.