For on thing an agent should never recommend against any kind of inspection and for another radon tests have been few and far between over the last century or so and no one really knows where all of the pockets of radon gas on the planet are or how many homes may have high levels of radon in the basement.
Home buyers should not let anyone talk them out of any kind of inspection. Sure inspections may slow down the sale process but they protect the buyer and the seller and any agents involved in the transaction.
Even with inspections it is possible to buy a home and find out about some problem after the fact. There is risk involved in buying almost anything.