It probably means to let them know if you need anything but not like actually anything but you know just about anything else. You dig?
Any questions? Let me know if you need anything.
Edit: dude in all seriousness we can't answer this without know who this is. Of course some people are just telling you to piss off, some are exchanging pleasantries and some are actually authentically nice. How the hell can we tell you that over the internet????