I think it is a very poor (automated?) translation from the German, and I've been trying to figure out what he actually means by "forget to stolen"..... my best guess is that he's telling any "members of the criminal fraternity" who may look at the listing not to think about trying to break in to his premises to steal the expensive loco, because it is kept in a secure safe...... I know that sounds odd, but maybe he's had trouble with break-ins in the past. Of course I could be totally wrong!
You could build a lovely model train layout for the kind of money he's asking for his one locomotive. High prices are not unusual with collectors, however. There is a 1964 Volkswagen Beetle for sale over here in the U.S. for one million USD! It's like new and has on'y 23 miles on it, but really, it sold new for $1.995 plus tax and license. LOL.
It's worth a punt. You never know, he might just have set up the auto accept on the make offer option incorrectly. He'd then be legally committed to sell. Only one thing though - you can't make a 'best offer' to include postage.