1. There is no question that 'bribing' is unethical and illegal. However, nowadays there are a lot of developing countries in which corruption and bribing is a common practice and large companies that are targeted to expand to those countries' markets have no other option but to pay government officials or other demanding individuals. In the Siemens case which involves bribing for contracts it is partially understandable if the company's convicted managers were not the ones offering the money, as they claim, but the ones who had no other choice but to pay or avoid the market at all. For example, I am quite familiar with the ways business is done is Russia and I can assure you that bribing cases are very common there, with number of them being literally unavoidable. As for the case with bribing Wilhelm Schelsky, the chairman of the AUB labor union, I think it was completely unnecessary for such a big and respected company like Siemens to do that. Such bribing is certainly avoidable and it is not worth for the company to risk it's reputation. In my opinion, it should be a concern of governments to prevent such actions and create mechanisms that make any types of bribing activities impossible, especially in companies in which the state owns a controlling stake.
2. I think if a company has a respected name in the field, offers competitive prices and meets all qualifications to win a contract, then it has couple of options to do so without bribing: a. Status of a well-known and respected company gives it an ability to contact the government officials and local analogue of U.S. Securities and Exchange Commission beforehand and ask to monitor the process of tendering. b. If the contract is for a large amount of money and, maybe, socially important, it might be a good idea to attract the media to the deal.
I believe these two options would scare away any company managers who are intended to benefit from bribing.