You know in PoA, the manager of Flourish and Blotts really causes himself trouble by assuming Harry needs the Monster Book of Monsters, and goes straight for the cage. It's only required for Care of Magical Creatures, so based on his actions/assumptions, imagine the stress he goes through, only to realise his efforts weren't required?
The Weasleys stand up for themselves win lose or draw, that’s always been clear. This would’ve been an awesome scene and set up the context for the Malfoy’s pure blood supremacy and Arthur’s fierce defense of Muggles, Muggleborns, and his family.
It's established very early on in Chamber of Secrets that Mrs Weasley is a big Lockhart fan. Undoubtedly his appearance and book-signing would have been advertised, probably in Witch Weekly or the Daily Prophet. I'd wager that Mrs Weasley planned their trip to Diagon Alley in advance for the same day.
That's probably why they ran into Hermione, too. It would be a massive coincidence otherwise. We know that Dobby was intercepting Harry's letters from Ron and Hermione; it's probable that they were in touch with each other and Ron probably told Hermione when they were planning to go to London and pick up their school supplies.
There was a thud of metal as Ginny’s cauldron went flying; Mr Weasley had thrown himself at Mr Malfoy, knocking him backwards into a bookshelf. Dozens of heavy spellbooks came thundering down on all their heads; there was a yell of ‘Get him, Dad!’ from Fred or George; Mrs Weasley was shrieking, ‘No, Arthur, no!’; the crowd stampeded backwards, knocking more shelves over; ‘Gentlemen, please – please!’ cried the assistant and then, louder than all, ‘Break it up, there, gents, break it up –’ Hagrid was wading towards them through the sea of books. In an instant he had pulled Mr Weasley and Mr Malfoy apart. Mr Weasley had a cut lip and Mr Malfoy had been hit in the eye by an Encyclopedia of Toadstools. He was still holding Ginny’s old transfiguration book. He thrust it at her, his eyes glittering with malice.
It would have been such a good scene to have.
