Web ads with drastically different clarity, apparently same specs

[PG in LA]

I just posted an ad with photo and text to an online newspaper, and the specs required were really low. They wanted a jpeg, 300x600pixels, no larger than 75 KB. The text looked predictably awful, so they said their art department would reduce it for me, but it looked just as bad. There is small text, often in a color, on another solid color, with some white text on a solid color. In rotation with my ad is another, that has 6pt type that looks immaculate. Some is dark on white background, but some has white text on a solid color, much smaller than mine. Their art department swears the file specs are the same, but I have never seen a jpeg that crisp. Any ideas what the secret might be? Thanks!

[c.pfaffenbichler]

Could you please post screenshots of the two ads? 

Have you downloaded the other ad, to verify its format and pixel dimensions? 

[PG in LA]

So sorry, I didn't get the notification from this! The image saves as a WebP image, I haven't downloaded the plugin (and use an old Photoshop version). Any other way to find out its specs? Thanks!

[PG in LA]

Apparently I can't attach a Webp file; here's the screenshot

[PG in LA]

Using "inspect accessibility properties", I can see that the clear ad is listed at 1250 x 2500 pixels, scaled down 50 percent. That is a lot larger than the requested 300 x 600 px. Unfortunately, my ad is done running, so I can't tell if there was a difference. I have no way to know if the online newspaper makes the webp conversion, or if the other advertiser provided it. It was not offered to me as a file option, only jpegs. Bummer.