re: Can a dealer give you a trade in value without seeing the car in person?

Not really. I shop around a lot (find every dealer with the car I want within a 500 mile radius). I research the black book/nada/blue book values, etc. And I'm only dealing with the dealers who are giving me an excellent price on the new car, so it's not like they are making it look like I'm getting a good trade in value while they jack up the new car price. I'm sure it's more difficult if you're trading in an old car with issues. But trading in a car that is just a few years old and still looks new, they'll give you a true value to make a sale. Now if you get there and they find you misrepresented your car's condition...
I always clean the car up well and send LOTS of pics.

Also, I don't try to screw the dealer either. I had one trade with a crack n the muffler, but the exhaust system was all one piece - $1,700 to replace. I could have left it and hoped they didn't notice the sound it was making, but I replaced it after I had a deal made.
Informed the dealer and told them I was replacing it before the trade. They were fine with it. Honesty goes a long way.

The first couple times I did email trade-ins out of state, I was amazed at how easy it was and how quickly I got excellent deals compared to local dealers - far less hassle than going to a dealer in person.