Buying specific part variant on BrickLink I've ordered a lot of pieces (at least a lot for me) on BrickLink, among them a bunch of "3794b - Plate, Modified 1 x 2 with 1 Stud with Groove (Jumper)". Instead of that variant, I received "15573 - Plate, Modified 1 x 2 with 1 Stud with Groove and Bottom Stud Holder (Jumper)".

I've checked the order again, and the description for that piece reads "Plate, Modified 1 x 2 with 1 Stud with Groove (Jumper) We do not differentiate between 3794, 3794a, 3794b and 15573!". I missed that part, so I know this is at least partially my fault (it's not too bad though, my MOC will still work, but if I had needed 15573 and gotten 3794b it might not have).

So my question is, is this just another thing I have to look out for, or is this a really bad practice and should not happen on BrickLink?
I'd say this is something to look out for when dealing with a part that BrinkLink itself notes is very similar to other part numbers.  Reading the detailed notes about buying sets is more important than parts generally.  I'd read a bit more closely about the stated condition of used parts than new parts.

I've made a few dozen orders on BrickLink over the years and I haven't run into this exact situation.  Yet any issues I've had have been easily resolved by contacting the seller.  I wouldn't pester the folks that say they treat them all as the same part, but you can probably find somebody out there who will give you exactly what you want.  Find another seller, read to make sure they don't have a similar warning, and drop them a note to make sure everybody is on the same page.