I don't buy the complete series at once. I do like to wait until the series has been finished because I've spent decades waiting for a new book to come out. But I buy the books one at a time just in case the later ones aren't as good as the first then I can just stop reading them and not have the rest of the series they're sitting on my shelf.

I don’t - moving books is such a pain in the ass. My physical book collection trends to shelf pieces and I end up reading them as ebooks.

I like to do a lot of research and then buy the book outright. I mostly read standalone novels even though my favorite two genres are sci-fi and fantasy. Also, I am a slow reader. The only times I will buy multiple books at once is when not doing so will cause me to not get a matching set of books. I much prefer hardbacks or at least trade paperback over paperback copies.

Also, I tend to give books away when done with them. I don't want a huge collection of books for when I move.

I won't buy a whole series unless I've read them all and loved them. I've been disappointed too many times.

I will buy them as I read them, not all at once

I rarely buy the whole series at one time, but I also set a rule of not buying a book until I'm ready to read it. I almost did with the Wheel of Time series because the library waitlist for the books was months long, I'm so glad I didn't because I quit after book 4 of I think 20.

I have the bad habit of being a completist and will buy the whole thing before I even read the first book. Some series that I’m not as sure about I may get as ebooks as they go on sale.

Yes, that's exactly how I do it

Unless I hear otherwise, and then I will take a chance on the next book and see if it's better.

When it comes to series-- especially long ones-- I tend to buy the first 2-3 books at a time. Once I get past about book 4 is typically when I decide whether or not I want to purchase the entire series. And when the quality of the sequels are just as good as the first? Then hands down I'm buying as many at a time as I can afford (I've only done this maybe 2-3 times).

With the advent of ebooks and online shopping I buy books as I read them.

In the old days when I had to physically go to the book store I bought entire series at once (and occasionally regretted it).

I'm quite dumb and I tend to buy whole series in one go based on recommendations from random people I don't know. I most recently did this with Cixin Liu's Three Body Problem trilogy. I felt quite the fool midway through the first book, groaning and tutting at page after page of utter dross, knowing I had two more to go through.

I am kind of weird and am averse to owning a book unless (1) I know I will be rereading it often or (2) I have not read it yet and know I will donate it after I finish reading it.

Otherwise, I like to support the local library and read there.

I have never once bought an entire series prior to reading it. I rarely even buy two books in a series at once, unless I thought the previous books were exceptionally done and I wanted the whole thing - usually happens with a really good first book of trilogies. Recently that has been me buying the #2 & #3 of The Poppy War trilogy and the Masquerade trilogy.

I buy as I get to each book in the series.

Except for Discworld. If I'm reading a series that's 40 books long and I've enjoyed 10 of them, I'll buy them up quickly to make sure they all match on my shelves. Usually when there's a big sale.

I tend to prefer ebooks now though. Cheap/free and doesn't require effort to move. If I LOVE a series I might purchase the print copies after (did this with The Witcher).

I buy them as I read them, this way if I decide to stop, I'm not stuck with the rest of the books I'll never read

I have historically always read the entire series before purchasing.

Basically a safeguard against buying a whole series because the first book or books were good, but then being disappointed later if the series runs out of steam.