I don't know what dealership you're working with, but I've sold cars and it's a pretty simple process. You just have to play along. When you're ready to make the deal, decide how much you're willing to spend. Would you take the deal, right now, if they gave you 7500? Are they giving you anything off sticker?
It works like this... you've got the dealer invoice price for the car you want to purchase. You can look up invoice prices on edmunds. It doesn't matter if they have the particular car that you want on the lot, every significant manufacturer has an online system where they can view other dealerships' inventory and make a trade for one of their cars for one that you want (keep that in mind, if they're pushing you to this white car they have NOW instead of the silver one you really want - if you're willing to wait a couple of days, your dealership will bend an awful lot if you let them feel like you're getting closer, including working out a dealer trade of cars when it comes time to sign). Anything over the invoice price (MSRP) is profit on the vehicle in and of itself. Japanese manufacturers have far less markup on their vehicles to stay competitive with the cheaper American cars, that's just how it goes; so don't expect to get much money off the sticker. Kelley Blue Book's trade-in value (assuming the car is in good condition) under the good conditioned category is generally very, very close to the black book value of your car. The Black Book Value is a documented auction price of your vehicle in your state. The vast majority of states have this, New York included. They can look up any manu/model by year and see how well this car has done at your state's automotive auctions over the recent course of time. This is the benchmarking guide for dealerships to know how much they should be willing to give you. If your car is in nice condition, they will try to sell it retail on their lot; but if it sticks around for a while, dealerships get paid kickbacks and incentives to move cars off the lot, so it goes to the auction.
If you want 7500 for your car and that's what kelley's "good" says it's worth on trade; call your salesmen, tell him you want to do the deal right now, and you'll only sign if you can get 7500. I don't know if lying is in your repertoire, but telling them that another dealership has offered you 7500 and you're close to signing with them will provoke a much less aggressive response, in general. Good luck
A second trade-in doesn't have to be a bad deal, but you really have to work through your figures and scrutinize to make sure you aren't screwing yourself, because then they have even more leverage in terms of pushing the numbers around.
edit: make sure you ask them if there are any incentives on the models you're looking at. Any rebates? Are you financing? Special rates? That pretty much covers most of the variables you're going to be toying around with. You can look the incentives up on the manufacturer's website or on edmunds, as well, generally; although your dealership will be more up-to-date as it is typically updated monthly.