"The Roman contract of sale is consensual, bilateral, and based on good faith. It is perfected by mere consent, without the need for form or delivery of the thing. The seller's main obligations are: to keep the thing safe until delivery, to transmit peaceful possession, and to be liable for eviction and hidden defects. The buyer must pay the price in money."
If you are looking for a topic to write about or need a specific angle, these are highly relevant modern discussions in Roman Law: pdf derecho romano