There's an exceptionally (no, pretty much 100%) good chance the ebay barlow was dodgy as. Especially if the whole setup you bought was only $50. That big black dot in the centre of the image of Saturn would've been the off focus image of your scope's secondary!!!!. How long is the barrel of the barlow???. You can get short and long barreled versions of barlows, which will vary your length of travel for focusing...depending on the eyepiece you're using. Sounds like you weren't able to bring the eyepieces to focus using the barlow you had. If you want a barlow, get yourself a decent one to start with...even if it costs $200 or more. At least you'll have a quality optical piece that will do the job you ask of it. Although, you can get reasonable barlows for $80-$150....try these,
http://www.myastroshop.com.au/products/barlow.asp
https://www.bintelshop.com.au/welcome.htm
http://118.127.11.230/catalog/index....sort=4a&page=1
They'll have what you want, and then some
