Final answer:
An unlicensed real estate assistant at an open house is prohibited from negotiating the sales price with potential buyers.
Step-by-step explanation:
An unlicensed real estate assistant at an open house is prohibited from negotiating the sales price with potential buyers. This responsibility should be left to a licensed real estate agent who has the proper training and knowledge to handle negotiations. The other options, such as greeting potential buyers and providing basic property information, collecting contact information for follow-up, and assisting with setting up marketing materials, are generally within the scope of an unlicensed assistant's duties.