I once worked at a small company that was a vendor for a big company. My supervisor knew that the contract with the vendor would be ending some time that year but she proceeded to hire me without telling me of such. I would not have joined had I known.
Unlike her predecessor, she was known to bend over backwards to every request of that big company no matter how unreasonable it was to the company that hired her.
After a few months she resigned and I came to know that she got a job with the big company.
I eventually deduced that she was so accommodating to those requests because she didn't want to burn bridges. Somehow it worked out for her.
However, is it right of her to do so and is it right for the big company to hire her?
Since her previous company was the one who paid her salary, isn't she obligated to work in a way that benefited the company instead of herself?
Also, shouldn't hiring managers be wary of hiring anyone who is from a vendor company? This is because such people (not all, obviously) have proven that they will put their self-interest ahead of the company. Such people are no different than traitors.