Yes ditto. Happens a lot.

I can understand why people do it but it goes against the spirit of curation. Also it puts undue pressure on the other person to vote for you.

Particularly if you just say "upvoted now please check my mine out" - that basically tells you the upvote was purely for getting yours and they don't give a crap about your post - probably didn't even read it.

Even if that is what you are after a better strategy (to avoid pissing people off) would be to make a serious comment on the other post - it will encourage people to check out your posts themselves and without any undue pressure.

The unsolicited dms are pretty annoying. It's fine when I know someone really well and obviously if I ask for the link and they dm me - that's how it should work. Some people think it is OK to just spam complete strangers with their new posts repeatedly. That's what the links chat channel is for.