I have recently noticed that yahoo finance and google finance provide different closing prices on some stocks. For example, the previous days closing price as of 10/9/2019 for DAL is listed as $53.20 at https://finance.yahoo.com/quote/DAL?p=DAL&.tsrc=fin-srch. However, according to google finance the previous day's closing price is $53.18. Sometimes however the two prices match, but sometimes they are different. My question is why is that? I was expecting them to always be the same.
$53.18 was the last trade of regular hours. $53.20 was the closing auction. The closing auction is generally treated as the official close.
Google is wrong - elt894 has a good explanation. The closing price auction is always the close price for both the primary exchange quote and the consolidated tape quote, or the prior eligible trade if nothing trades on the auction. Yahoo is garbage - repeated dividends, splits that don't exist, missing splits, repeated values, incomplete history, incorrect corp actions. Both have survivorship bias too.
I've seen then quote penny stock at insane prices, like tens of thousands per share ($22k+ for the last one I saw, as I recall.) Also, crazy random numbers in the company financials. Not saying they're totally useless, but not exactly "top notch".