In principle what Pappnase has told you is correct, but his is the practical version, and deviates in detail from reality.
That the buyer pays the cost of conveyance is enshrined in law - I can't remember which, but will dig it out if required. The contract, whether it stands or falls, belongs to the act of conveyance, so it's the buyer's responsibility. Having been bitten too often in the past (yes, Notaries also get bitten) they tend to include a clause in the contract which, as Pappnase said, binds both parties, jointly and severally. In practise, following a failed contract, the Notary would bill the buyer. Only if all means of obtaining payment fail, eg. if in reality the buyer turns out to be insolvent, then the Notary would bill the seller, and would be supported by the courts in all efforts to obtain payment.
A tip for those not fully au fait with Germany's ways: virtually everything is governed by law, and the way to solve a legal problem is to refer to the basics, i.e. the law governing the matter in hand. Only then can you know if your aim is achievable, and how to set about getting to it.