Recently my brother in law has bough a scooter to get to and from work, he took it to the bike mechanic and the mechanics basically turned round to him and said the engines seized and its gonna cost £1000 to fix.

How long would an engine actually take to seize? He's had the scooter about 3 weeks and what can they do about it to get their money back as its not worth the £1000 to fix? thanks