Switching from synthetic back to conventional??

My friend just bought a used car from this guy and was wondering if the rumors were true or not that once you change it to synthetic you cant go back. Me personally i would keep synthetic in it. Thats what i always have run in my engines. But this guy is cheap and doesnt want to spend the extra money!! Any ideas???

 

i heard with the way both are now, there isnt a problem switching back which is why i am running it and kinda seeing what happens with that or whatever. i dont know if ill switch back but a selling point was that i could. but thats what someone said, who heard it from someone, who also read it online somewhere (probably) so someone might chime in who knows better

 

im pretty sure it is true
but a quick google search proves me wrong
http://www.popularmechanics.com/automotive/how_to/4213451.html

 

why do they still make regular oils for cars?....just make all synthetic like mobil 1 does ....even though it has some regular base oils in it