I Only Have Eyes For You - S2-E19
Visible crew/equipment: After the history teacher writes, "Don't walk away from me, bitch!" on the chalk board, Buffy says to Xander, "I'm telling you, something weird is going on." As she says "something", a boom mic is reflected in the window behind her on the right.
Revealing mistake: When Buffy is walking alone into the desert, a man's legs are visible in the upper-right corner of the frame and remain visible for a second or two. (00:03:35)
Deliberate mistake: Every time the commandos are seen in the early episodes of this season (The Freshman and Fear, Itself) they wear ski masks to protect their identities. Starting in The Initiative, they stop doing this. The reason is that the audience needs to be able to identify the different commando characters, but it's still a discontinuity.
Visible crew/equipment: In the episode 'This Year's Girl', when the Scoobies find the demon in the woods that Adam has cut open you can see a boom mike operator in the background. (00:07:40)
School Hard - S2-E3
Continuity mistake: When Spike appears at the Bronze and lures Buffy outside, she runs past her table which has her jacket on it. But once she is outside she suddenly has her jacket on.
End Of Days - S7-E21
Audio problem: When The First lets Buffy get away with Caleb's scythe, Buffy jumps back up the trap door but we don't hear her touch the ground as she lands.
Revealing mistake: When Sid stabs Marc after he has transformed, there is no blood on the knife that he uses afterwards.
Continuity mistake: In episode 'Same Place, Same Time', Gnarl cuts Dawn across the stomach paralysing her and ripping her shirt, but when Buffy and Xander are carying her home there is no tear in her shirt or any blood. Also when Buffy goes back to kill Gnarl he tears her shirt but seconds later the rip has gone.
Audio problem: When everyone is in the Bronze - just before the vamps show up - you hear the first line of a song being played, Ballad For Dead Friends by Dashboard Prophets, cut to outside and you see the vamps strolling along and killing the doorman, then cut back into the Bronze and the same line plays again. This is a total error in cutting the show, it is stated there is no live band but still the same line plays twice when that is not how the song goes.
Other mistake: In the episode 'Anne' Kenn tells Buffy that time in his hell dimension passes more quickly, that one day on Earth is the same as 100 years in his dimension. This means time goes roughly 36,000 times quicker. When Lily falls into the portal, it's at least 10 seconds until Buffy jumps in after her, but Lily is still just sitting there looking stunned. If times moves that much faster, 10 seconds would become over 4 days. Would Lily still have been just sitting there?
Continuity mistake: In the last episode of Season 5 we see Spike thrown off the tower by Doc. Spike somehow manages to change from black trousers and boots into blue jeans and white shoes mid-air. He's back in black by the time he hits the ground. (00:35:45)
Continuity mistake: In the season five episode Triangle, Anya says she has never driven before, but in Graduation Day part one she tells Xander she has her car right outside. (00:22:50)
Continuity mistake: In the episode Prophecy Girl, during Buffy's rooftop fight with the Master, her shoes change in between shots from white heels, to black boots when she's kicking him, back to white heels. (00:41:35)
Audio problem: When Buffy kills the vampires dragging Xander at the beginning, we hear two impact sounds but don't hear either of them turn to dust. They were only a few feet away and there was no other sound to cover it up. (00:01:00)
Never Kill A Boy On The First Date - S1-E5
Continuity mistake: When Buffy is talking to Owen at the end, there is a woman wearing a red/black checkered jacket, sometimes carrying a red bag, walking up the stairs behind Owen several times. You can also see her behind Buffy in shots facing her. (00:40:25)
Chosen answer: From what we see in the series, certain girls are identifiable as potential Slayers - Kendra clearly fell into this category. The identification method is presumably mystical in nature, but the Watchers' Council are pretty effective at that sort of thing, so they're quite good at tracking down the potentials ahead of time. Not perfect, though - it does appear that Buffy herself may have slipped through the net - certainly she had no inkling of what she was until she'd already taken on the role of Slayer. It is possible, however, that this was actually cultural - an American family would hardly be likely to turn over their daughter to some strange man for 'training', so the Watchers might have chosen to keep an eye on her covertly, whereas some other cultures (like Kendra's Jamaican parents) might be more willing to believe.
Tailkinker ★