I would never buy a Samsung galaxy phone during its launch. Samsung’s resale value drops like a rock, about 50% after the first month.
“Based on the depreciation patterns of the S5, S6, S7 and S8, musicMagpie has revealed that
the S9 will likely lose a whopping 50% of its value in the first month alone. Samsung’s previous flagship device, the Galaxy S8, which had a retail price of £689, lost 49% of its value in the first month after launch, and then dropped by another 2-3% every month after that. By nine months old, it had lost 65% of its value.”
https://www.alphr.com/samsung/1008532/samsung-galaxy-s9-lose-half-value
And with reports that the s10 sales is coming in below last years disastrous s9, resale value might plummet lower and/or faster when compared to previous galaxy phones.
Another prediction that the s10 will lose half its value after the first month.
“bankmycell comes to the conclusion that the S10 will follow a similar trajectory, with an expected value depreciation of about half its value after the first month of its release.”
https://www.xda-developers.com/samsung-galaxy-phones-value-depreciation-iphone/
iPhones dont seem to suffer from the same drop in value
“Focusing on the latest iPhones, it looks as though the iPhone XS Max lost 15 percent of its original resale value through the first quarter of retail availability. The iPhone XS lost 13 percent while the iPhone XR dropped 5 percent. “
https://pocketnow.com/iphones-over-galaxy-launch-earlier-trade-in