Your scanner output resolution should be 75dpi which is more or less an internet standard (if using a printer the higher dpi the better).  The change from 300 dpi to 75dpi  will give you a 16x reduction in size ie 16mb to 1mb.   Also I don't think eBay will let you upload png only jpg.  If you are using your own hosting png is ok just not uploading to eBay.  The new rule for Ebay photos is min 500px longest side however the optimal they suggest is 1600px.

Snipping Tool - best ever invention ! 🙂   Clear image, easily downloadable, jpg, awsome

Actually, you have a point! That thing is so damn good!

I never thought to use it for my eBay pics though. I will now however 😄

I don't use Paint. If I am not using Photoshop I am using one of the nifty image editors that is available for free on the internet.

I don't like to go any bigger than say 700 pixels on the longest side. You don't want postage stamp sized images online but you also have to keep in mind that some people (yes!) are on dial up or don't have wonderful lightning speed internet. When I am saving for web it is generally 72 dpi (dots per inch).