Advice: Silent Pick-ups?

As a commissioner, I've always thanked my artists for the lovely work they do; it's just common courtesy. Still, I was a bit surprised when I saw artists complaining about silent pick-ups in the past. Yes, it's rude to accept your commission without thanking the artist, but it didn't seem worth the fuss some people were making.

Now, I've only started opening for commissions within the past year or two. It's rare that I'm commissioned, but I'm grateful that my customers have always been friendly and understanding throughout the process. Still, half the time, my commissioners (usually one person in particular) just pay me after I e-mail them the completed work – not even a quick "thanks" to accompany the payment. And, well, I was startled (and, honestly, a little embarrassed) by the extent to which that irritated me.

So, I guess we get to my questions. Are silent pick-ups commonplace, in your experience? Do you hardly notice when they happen, or do they influence your readiness to work with certain commissioners again, especially if they've done it more than once? I'd really appreciate any advice you all have!

Edit: Thank you to everyone for your advice! I've received some excellent feedback from you all, including how to approach these situations more positively and professionally.