I'm going to be scrapping an 80s model car shortly, how can I be sure the scrap yard is giving me top dollar for the metal?

Could you call around to other local scrap dealers to find out what the going rate might be?

Depending upon whether it is driveable, you can donate it and take the tax write off. You just need to determine if the write off is worth more than scrapping it.

call Ahead and see what there paying for Scrap per ton,,Then when you take your scrape in the will give you a weight slip so you will know what it wieghed.
But some places just pay a flat rate for old cars,,,So just call around that will help ;)

scrap value of your car is only $50

you're not going to get top dollar for metal right now because the price of metals right now is seriously low. Why? check out all the steel making plants that are closing or operating at 50% capacity. Nobody is buying steel right now. At least not in significant quantities. The economy has slowed down THAT much.
I just saw a documentary about this and now I understand why I'll have to wait a long time to take in my recycled aluminum before I get some decent $ for it. I drive by a metal recycler every day on the way to work and last summer the price of aluminum was twice as high as it is now, so if you want good money for it:
1) part it out, someone might need some parts
2) donate it, they might auction it off for a charity.
3) just get rid of it and take the loss, and thank our fearless leader for the change that you can believe in (read- financial black hole) he just dug even deeper.

We discovered that the write off on our taxes for donating our old car was worth far more than the recycle value. The donation center came out and towed it, and we recorded the donation receipt on our taxes for the savings.