Is it possible to create a subjective trading system (for eg: second hand goods like laptops, television cell phones etc) using concepts of bitcoins and smart contracts. Payments on the system would be staggered in stages. To give you an example lets Assume Alice wants to buy a second hand Television in the budget range of 100$
STAGE A: In order to participate in the trading system, the user Alice will first have to deposit an Amount equivalent to say 5$(or she may depisit the Bitcoin equivalent of 5%). This amount is refundable at any given time however the significance of this stage is that if Alice chooses to withdraw this amount, she will no longer be able to participate on the platform and view listings available on the platform. So in a way the money put in at this stage is to filter non serious participants and to remove stale and duplicate listings.
STAGE B: Once Alice has browsed the platform she shortlists three televisions that she is interested in. In order to send her offer to their respective owners, she has to increase her deposit to say 100$ (which is roughly the price of the television she wants to buy). Once she has put in these 100$ she can start parallelly negotiating with various resellers. The significance of the 100$ put in at this stage is that the counter parties of Alice who are selling the television know that Alice is a serious buyer and also has the capacity to pay for the television. Again if alice chooses to withdraw the entire amount she will drop out of the platform. If she lowers her deposit to the amount that was existing in Stage A i.e. 5$, she will not be able to actively negotiate with the sellers.
STAGE C: After parallelly negotiating with multiple resellers Alice finally decides to purchase the second hand television from Bob (the seller), the price finalized between them is 90$. In such an event in order to make sure that the sanctity of the transaction is maintained and both parties honour their commitments, both Alice and Bob enter into a escrow transaction where the 100$ deposited by Alice in stage B are pledged into the escrow. After successful closure of the transaction, 90$ are given to Bob, say 2$ is earned by the platform for facilitating this trade and remaining 8% get refunded back to alice.
Now the question is how can we implement this using bitcoins & smart contracts.