The Soviets fought Japan in two major border incidents throughout the 1937 - 1939 period in China and Mongolia. Included in these were:

Changkufeng / Lake Kasan 1938. Both sides took several thousand casualities. The Japanese were forced to withdraw their troops from this area, at least temporarily.

Nomohan / Khalkhin Gol April 1939. Again, both sides took heavy casualities. But, the Japanese 23rd Infantry division was destroyed in the fighting (just over 70% casualities). The Japanese Army Air Force also took heavy losses. These were serious enough to force a major revision and expansion of pilot training to replace losses.

The Japanese had some rude shocks in fighting the Soviets in these "incidents" as well. They were totally unprepared to handle the masses of Soviet armor used. They were badly outnumbered in artillery and had virtually no means to counter the lavish use of this arm by the Soviets. Their small very professional airforce proved unable to cope with attrition and quickly was reduced to near uselessness. Japanese bombers proved unable to cope with Soviet fighters and their small numbers and bombload made them marginal as an offensive weapon.
Doubtless, Sakalin Island could have been taken by the Japanese at a fairly high cost (the Soviets recognized its importance and heavily garrisoned it). The problem is that they would likely lose large chunks of Manchuria in exchange, along with the resources in those areas.
I don't think the trade was appealing.