A GmbH would need to have proper accounting, all liabilities would have to be in the books. Anything else would be fraud and that’s one of the things that suddenly pierces the veil of the limited liability for the CEO (whether you can extract any money from the seller is a different, albeit related question) Do your diligence. You could also make the personal liability part of the sale. On the upside, buying a used GmbH may come quite a bit cheaper if the company owns no assets: the initial 25k are not a minimum that needs to be kept, they can be spent on things the company needs, so you might be able to pick up an empty shell for far less than that amount.

I’d not buy a GmbH from a random person on the Internet, but if you’re in a hurry to get a GmbH set up, there are notaries and lawyers that specialize in selling ready-made GmbH shells.

You’d still have to get the sale notarized and probably need to jump through a few hoops to rename the company to something suitable, but there are a few reasons that may be attractive, primarily that it offers limited liability from day one. Quite a few people forget that in the intermediate phase between notary and confirmed registration (GmbH in Gründung) the shareholders are personally liable for all businesses and contracts that the company enters into.

Normally you would have an accountant you trust, (i would highly advice against trying to do GmbH paperwork yourself) he/she would get directly in touch with the company that does the current tax and accounting work for my GmbH and do the vetting for you. Germany has very strict publication and documentation laws for GmbH's so there is not really some hidden liability possible, if there was that could get me to jail even if i wasn't trying to sell the company...