Commission for Sale of Service vs. Purchasing Service from Provider

We have partnered with a trainer that will come to our facility and lead small groups - for example, (4) 1 hour sessions on a Saturday.  My company accepts payment, provides the facility, promotes the event, etc.  He facilitates the training.  We charge $100 per attendee and divide the income 50/50.  I'm debating which is the better option: 1)Record the income as a Sale of Service and pay the trainer a commission of 50%. or 2) Purchase the service from the trainer and treat the the payment to him as COGS.  Any thoughts?