Legitimate power in negotiation can arise from different sources:
* Position power (authority from role/position in the organisation).
* Referent power (influence from respect, charisma, or relationships).
Reference: CIPS L4M5 (2nd ed.), LO 3.1 - Sources of power in negotiation.

Trust is the expectation that the other party will behave in a predictable and mutually acceptable way. In inter- firm relationships, the presence and absence of trust can affect the level of cost in a relationship. The existence of trust is taught to lower the transaction cost in a relationship. Dr. Mari Sako identified taxonomy of 3 types of trust in commercial relationship, which is very useful from the perspective of procurement.
Contractual trust: Trust based on the contract with TOP. This is potentially the weakest source of trust if there is nothing else to base the trust on, but it is the quickest to establish.
Competence trust: Trust based on TOP's professional qualifications or proven or certified technical capability or experience.
Goodwill trust: Trust based on knowing TOP has your interest at heart and will not behave opportunistically.
This is potentially the strongest type of trust, but it takes the longest time to build.
Otherwise, trust also has legal meaning. A trust is a legal document that can be created during a person's lifetime and survive the person's death. A trust can also be created by a will and formed after death. Charitable trusts are trusts which benefit a particular charity or the public in general.

Trust-building behaviours are as following:
Joint-effort issue resolution
Open sharing of information
Open and honest discussion on root cause of failures
Joint planning focusing on value for money and risk sharing
Commercial transparency and co-proposition of cost reduction and service improvement programmes Joint recognition and celebration of successes

Knowing supplier's fixed and variable costs is beneficial for the buyer in a negotiation. With these insights, the buyer would know the volume at which the supplier reaches break-even points and then offers significant discount due to economies of scale.
Reference: CIPS study guide page 80-81
LO 2, AC 2.1

There are 5 key phases of negotiation:
The opening phase: confirm understanding and get the issue on the table The testing phase: check assumption and confirm understanding The proposing phase: asking 'if' The bargaining phase: using tradeables The agreement and closing phase The testing could take the form of questions following a presentation by either side or questions on a tender or proposal document received by the buyer from the potential supplier. The testing phase is necessary to confirm that your approach and objectives are appropriate for the negotiation situation you now find yourself in. Careful listening, observation and interpretation of TOP's responses may give indication of the following:
Areas where TOP is willing and unwilling to make concessions
What factors or issues TOP places a high value on
If there are any non-commercial or emotional factors that may be pertinent TOP's underlying interests - why they are taking the position they are.