I'm long a 5pts vertical bull spread and I got filled at 5 to close out the position at expiration. Is this pretty common for getting filled at textbook theoritical value or I just got lucky? Right now the market bid is 4.8. Thanks!
There might have been some large-paper that took you out of your position. A local who was having a good day might have done a favor for the broker who wanted to get your order out of the deck and earn his commission-$.
It's possible. One time I got an excellent fill on unwinding a covered call. I was long 400 stock, short 4 20 strike calls. I got filled at a net credit of $20.05, I couldn't believe it, I put in the order for a net credit of $19.99. So yeah, getting filled at theoretical value, or even better is always possible, it's not a perfect market.