Doujins have been scanned without unbinding, resulting in skewing and some bleedthrough here and there. Work was done to try and reduce any glaring mistakes, but some things may have been missed.
Let's be real these doujins are so rare and cost a shit ton of money for each so I wouldn't mind the bleeding through. Heck last time I checked Inai Uchi's 1st Kirika doujin was like 10,000yen.
I would say yes and no. True there aren't many on sale on melobook or tora but you can get a decent amount at Comiket or Zesshou. unless you are talking about Adult doujinshi then yes those are both rare and costly.