@Lord Nemesis pretty much covered everything.
The guys at Agarwals - and other movers and packers - are experts at gauging the costs. They just look at your stuff and tell you how much it would cost. A few questions that you might want to ask are (in addition to above):
1) How they plan to pack certain items that you think are tricky / delicate. We had a fancy TV stand and center table and got them to explain to us how they would do it. Reason it helps is, they work based on certain assumptions, like parts are detachable etc. However, some of our items were apparently not. So they had to change the way they initially planned to pack.
2) Will they be disconnecting any of the electricals or you would need to get an electrician to do that. This is generally not covered by Agarwals, but is upto the personnel who come on that day to do your work. It is always good to ask in advance, and have an electrician at hand.
3) Will they be putting things back at the destination. The answer is yes, but confirm. They do assemble your stuff, and do a pretty good work at it.
4) Insurance. What is covered, and for how much.
For packing, absolutely remember to do this:
1) Be mentally prepared. Yes.
2) These guys work very fast. Very as in V E R Y. They bring with them loads of cartons, bubble wrap and tape and just wrap any damn thing that comes into their line of vision. They disassemble things fast, pack very quick, and shift them all at the end. Due to this, be sure to have done your own packing like clothes etc and all other stuff you would keep / carry with you BEFORE they arrive. You would not get time to do that once they start their work. Not that they don't co-operate, it usually is a lot of confusion in that case.
3) Special care items, supervise them while packing. Guide them on how you want them packed if you are not happy with what they are doing. Remember though that they are the experts, and they are trained. To give an example, our entire kitchen, glass and ceramics included, were packed by them, one piece at a time and put into the carton. I got my stuff intact. Not a single broken piece. Absolutely amazed. This is the norm, though there are cases when some things break. So get your super important stuff packed with better cushion.
4) The unsaid rule - be ready for some kharcha paani. These packing boys are grossly underpaid, deliberately or otherwise, and they expect you to give them a healthy tip as they know exactly how much you are paying the company for the transfer (one of them carries the bill). The tip is region based I have realised. So while 200 per head was accepted with grudge at one location, the same amount was considered big at the other place.