It's called an "excursion fare", which is meant for those that just ride the train without getting off and come back to the same station. You can talk to a BART station agent (assuming you can find one) and they'll let you out, or call customer service and they'll reverse the charge.
Modern fare systems should be able to figure out when you've exited right after entering and not charge you. BART is supposed to be adding a 30 minute grace period so if you go in and out of the station within 30 minutes, you won't be charged.
I get that they want to charge people who ride the trains for... fun?... and then get off at the same station, but it felt really silly.
“The San Francisco Downtown element of the Bay Area regional rapid transit system consists of a four-track, two-level subway beneath Market Street and a two-track, single-level subway beneath Post Street.”
“At Montgomery Street, the Market Street subway joins the San Francisco approach to the Trans-Bay Tube. The subway extends up Market Street to about Van Ness Avenue where it swings lo the south to become the Peninsula Line in Mission Street. The lower level of the subway provides through regional service by joining the Peninsula and the Trans-Bay Lines. The upper level is built to accommodate local rapid transit trains at a future time and will be utilized initially by the streetcars of the San Francisco Municipal Railway.” (emphasis mine)
And the flow map of estimated 1975 passenger counts makes it clear why they would want to double up on platform capacity along that stretch: https://www.bart.gov/sites/default/files/docs/50-years/1961-...
Imagine if we got this BART: https://i.imgur.com/hon9nEf.jpeg (1956)
https://tfl.gov.uk/fares/how-to-pay-and-where-to-buy-tickets...
And about refunds (typically you'd get an automatic refund for a one-off event)
https://tfl.gov.uk/fares/refunds-and-replacements/touched-in...
I always have high levels of respect for companies with such clarity
Having someone pay just to wave off someone is incredibly customer-hostile. Besides, how many people are even committing fraud like that?