You couldn't just go and sell stuff in the west. The USSR had exit visas. You had to prove you had a genuine need to leave, would be searched and treated very carefully. And proving a need to leave was difficult. Merely wanting to go on holiday or see relatives wasn't close to enough. There were very few exit visas available, which is why stories about defectors are often about elite athletes or sports champions.

https://www.rbth.com/history/334094-athletes-fled-ussr-how

Also the Soviets manufactured very little of anything valuable to the west. Their primary exports were commodities.