Unfortunately the trade-in value has nothing to do with Titleist as a brand.
Supply and demand plus the second hand market are killing it right now.
I have been looking for used AP2's for my son and good sets are going for nearly 1K, average sets are 800-900.
Try selling your slightly used gear to minimize loss.

Cheers,
Dr. K

Supply and demand. Same thing happens when you drive a new car off the lot. You will likely get much more for your TSi3 if you sell it yourself instead of a trade in. The trade in values are very low because most buyers for the new models are looking for new which means companies that take in trades usually have those clubs sitting in inventory for a while so they maximize their margins. Sorry you did not realize the full line of TSi's were coming out as a fitter would have been able to provide you that info along with ensuring that the TSi4 matched your needs. I know its a bit of a hassle to sell them yourself on-line but maybe you have a friend that would be willing to help if you don't have the time or don't want to mess with it. Good luck. Hope it works out for you.

I would definitely sell both those clubs rather than trade them in. I bought a TS3 demo when the new TSI's came out last fall for $250, went to trade it in and trade in value was around $130. I decided to just list it on Facebook marketplace and ended up selling it for $260! Now while I don't think you'd have the same luck, and it takes a lot of work on your end, you'd definitely get more of a return on your clubs than Titleist's trade in value.

i figured out the correct setting on my tsi3, B3 H1, i hit my 1st ever 370 yard drive (down hill down wind firm fairway, but still). i am so happy

In checking the blue book of club values, pgavalueguide.com, your TSI3 driver is worth $274 dollars and the TSI3 hybrid $122 on a trade in, if in premium condition. If they gave you $398 for the trade in that was a fair price, based on the blue book of golf clubs, which may not have been enough to purchase the used TSI4. A new one sells for $549.