Generic terms for people on opposite sides of a transaction [closed]

I'd like to find 2 terms to represent the people involved in a transaction. The transactions vary in their semantics, so I've had trouble finding a single set of terms. Here are some sample transactions and potential terms:

Give a Reward: giver/recipient  
Mete Punishment: giver/recipient  
Assign a Chore: initiator/assignee  
Ask a Favor: requestor/? 

The 2 terms will be used as variables in software code, and not exposed to users. I'd like them to be as descriptive as possible (x and y would work, but not be very readable), but generic enough to cover all the transaction semantics.

To complicate things, each person may be sending/receiving emails within the transaction, so I'm trying to stay away from "sender/recipient" to avoid confusion. The "recipient" of a request can be the sender of an email.

Some other terms I've thought of:

initiator/acceptor  
originator/terminator (kinda creepy)  
requestor/responder (not really precise)  

Any help is appreciated.

It's a bit "specialised", but some people go for transactor and transactee

The reason this is so localised is because it's often meaningless to attempt to differentiate the parties to a transaction. Neither necessarily has any specifically different role to the other, except perhaps in those cases where one gives goods or services, and the other gives money.

Traditional grammar offers two contrasting pairs: subject/object and agent/patient.

Perhaps requester and respondent.