I was considering doing small orders for powerleveling/questing for free for a limited time to gain feedback. Is this allowed, or do both parties need to contribute something for feedback to be given? 

yes, there has to be a risk for both parties for fb to be given

Edited September 20, 201510 yr by RDMerchants

It is allowed to receive feedback for a service, as long as the service was either paid or there was risk involved. An example for risk is doing a firecape service for someone, on an account that contains more than 1M RS3 GP or 07 GP. As we are aimed particularly at the RuneScape market, you are only allowed to give or receive feedback for graphics if there is at least $1 worth of goods (based off of common transfer rates) transacted. Feedback for free product will not be allowed. For further clarification on this rule, read here http://osbot.org/forum/topic/47264-feedback-rule-change/ If you use a middleman you may give him feedback but the middleman himself is not allowed to give feedback.