Is it permissible for a shop owner and doctors to exchange services and benefits, whereby the owner sells goods to them at cost or waives a small portion of their value in exchange for receiving assistance from them at the hospital?

If the facilities and gifts offered to doctors are in exchange for a special service and care that others who do not pay would not receive, then this falls under the ruling of forbidden bribery. The Prophet, peace and blessings be upon him, cursed the briber and the bribed.