How to fix thermal printer quality?

Question

I tried two brand new, different brand thermal printers. Both have poor quality with lettering and barcodes when printing shipping labels from ebay amazon and UPS. BUT, the test print pages look fine. 

I've adjusted a lot of settings like dithering, print speed, darkness with no resulting changes. 
The best way to describe the poor quality is it looks like dithering. But I have that set to 'none'. The edges of the barcode lines have "fur". The small font letters are blurry. The larger fonts have "fur". 
Again, the test pages with the printer info look good. Much better, but perhaps not 'professional/Amazon/UPS shipped' quality.
I am using labels from UPS.

Answer 1

Zebra ZP450 

and Bixolon ZRP-770III

(both from UPS)



If I leave the size alone (not adjust the margins), the label will print smaller and quality is even worse.



Anti-aliasing is not a setting that I could find anywhere.

Answer 2

Print the labels same original sizes, not bigger, not smaller.

Answer 3

Edit to add: have you downloaded the latest driver? 

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Which printer?  this looks more like Anti-Aliasing than dithering.  Check your printer settings for anti-aliasing and turn it on and set to 'smooth.'