Since model factories create in-memory objects, because of big memory usages it is not suitable for large seeds.

But you can use Faker for data generation:

use Faker\Generator as Faker;
class PostSeeder extends Seeder
{
    public function run(Faker $faker)
    {
        $users= collect(User::all()->modelKeys());
        $data = [];

        for ($i = 0; $i < 100000; $i++) {
            $data[] = [
                'body' => $faker->text,
                'image' => $faker->imageUrl(),
                'user_id' => $users->random(),
                'created_at' => now()->toDateTimeString(),
                'updated_at' => now()->toDateTimeString(),
            ];
        }

        $chunks = array_chunk($data, 10000);

        foreach ($chunks as $chunk) {
            Post::insert($chunk);
        }
    }
}

You could always create a private method which you call as you loop over each name in your array.

$factory->define(User::class, function (Faker $faker) {

    foreach($name in $names) {
        $this->customFakerMethod($name);
        // your logic here ...
    }
});

This function just takes the name as a parameter.

private function customFakerMethod($name)
{
    return [
        'name' => $name,
        'email' => $faker->unique()->safeEmail,
        'email_verified_at' => now(),
        'password' => '$2y$10$92IXUNpkjO0rOQ5byMi.Ye4oKoEa3Ro9llC/.og/at2.uheWG/igi', // password
        'remember_token' => Str::random(10),
    ];
}

So your users will be created in the order that you wish.

Make use of randomElement method

'type' => $faker->randomElement(['seller', 'buyer']),