Someone  asked me how to do this and I discovered that you can't have a negative discount percentage, negative quantity or negative price.  So this makes it impossible to do... well, no, but it is not quite as easy as we would like.  To make it work you need to create a Product and Service csv file to import to make it work.  Here are the step by step instructions on installing it and using it.

Installing the trade-in items

1.  Go to the BCM menu and select the Product and Services menu item
2. Press the import button at the bottom of the dialog to get the screen shown on the left  
3. Create a csv file on your desktop called tradein.csv (start / run "notepad %homepath%\tradein.csv")
4. Copy and paste the text below into the text file and save

Trade In (10000), Trade in, -10000 Trade In (1000), Trade in, -1000 Trade In (100), Trade in, -100 Trade In (10), Trade in, -10 Trade In (1), Trade in, -1

5. browse the csv file on your desktop and press import
6. Job done

Using the trade-in items in an opportunity

Now we have these line items, all you do is select them in an opportunity and use % discounts to make them fit.  For example, if you wanted to give £2,000 discount, simply add the trade in (1000) qty 2 to the opportunity.  You can add a higher number and then discount down, so for example if you want to add a trade in of £39,000 then you would discount by 2.5% and have a qty of 4 for trade in (10000) - see the picture on the left.

Hopefully this little kludge will enable you to do trade-ins.

ttfn

David