problems
* Asymmetric information

The initial contract can cover only short-term situations. Eventually, renegotiation is needed, which provides an opportunity for e.g. S to hold up B. As S knows that the investment is a significant cost to B and tries to use this as leverage to negotiate an increase in its prices. In that case, S has more bargaining power, compared to B, and tries to use it to its own advantage. The source of power lies in the investment of B. For B it is hard to find