The shop's manager is saying that the marked price of $70 is a "test of the market" to see whether there are customers willing to pay that amount for the desk. This suggests that the manager is open to negotiation and may be willing to sell the desk for less than the marked price.
The shop's manager may not be willing to let you have the desk for $40 because it is below their desired selling price for the desk. However, the manager may be open to negotiating the price and may be willing to sell the desk for less than the marked price if you make a reasonable offer.
It is also possible that the manager may change their mind about the price if the desk remains unsold for a long period of time. In this case, the manager may be more willing to lower the price in order to make a sale. It is also possible that the manager may be willing to sell the desk for less if you are purchasing other items from the store or if you are a repeat customer.