Some further notes ... By the way 'The Price ' a 1967 play by Arthur Miller is the only literary depiction of a house call in action that comes to mind- although it concerns a furniture dealer rather than book dealer. The dealer is called Solomon, an incredibly aged, incredibly wise antiques dealer, who has come, almost out of retirement ("You must have looked up my name in a very old telephone book"), to give a price for the furniture in the attic of a once prosperous Manhattan brownstone. Rather in the line of Ibsen and one of Miller's best plays... (image below with the aptly named Trader Faulkner as Solomon.)
HINTS AND OBSERVATIONS.
The dealer would be advised to arrive at the appointed hour, clean and, if possible, sober. He or she would be advised to avoid lunchtime as they may be asked to eat a meal which can establish a bond that makes it harder to turn the books down flat when they are poor stuff, which, sadly, is often the case. This bond could work in your favour - especially if the books are great and you are possessed of basic social skills and decency. However if you are anything like me the first thing you would want to do is look at the books and find treasures. Not a good idea to bring price guides as they can be seized by the seller and through misinterpretation be used against you. The best bet these days is to bring a cellphone and if stumped for prices or edition points etc., to "phone a friend" - hopefully one hooked up to the web and services such as ViaLibra.com, abebooks and ABPC.
When making an offer it is best to announce it confidently. As a very general rule of thumb it should represent about 40 to 60% of what you might eventually hope to realise for the books depending on their quality and how fast they will sell. It is worth leaving a little 'wiggle room' as sellers often like to drive a price up. Honesty is, of course, the best policy and a dealer who immediately doubles his offer on rejection or increases it dramatically is likely to reveal himself as a swine and a blackguard. In the case of lower price books where it takes longer to get a return a third or a quarter or less might be appropriate. It is generally best if possible to 'pick' and not be lumbered with undesirable books. Try to leave behind the 'dogs' and if forced to take the lot back out unless its really worth it, nowadays too much crap is a terrible burden. If you have to outbid some other dealer do not be afraid to ask what has been offered (half the time people will tell you) if it is too much do not top their offer but make a dignified exit and express an interest at a lower price if the deal with the other guy (possibly some extravagant, fly by night chancer or even a general clearance dealer ignorant of book values) falls through - and they often do. If you find you have (mentally) grossly exceeded the offer of another it is often worth looking at the books again in case you have overrated something (and vice versa.). Don't think because the seller seems to like you that they won't sell to another. Do not worry if you don't get the books--the world is full of them.
Take boxes and be aware of access. A load of quite good books on the sixth floor of a flat without a lift can become a real effort. We once cleared such a flat (8th floor Shepherd's Bush, no lift) and found it worthwhile to employ a chain of muscular students to pass the stuff down the steep steps. A friend in the Channel Islands recalls clearing a mansion on the tiny island of Brecqou ( or was it Jethou or Lihou? ) where the books had to be hauled down the cliff by ropes onto a bobbing boat and sailed back to Guernsey. To be continued with tales of dealers clearing books in sacks, notes on common mistakes and misconceptions, exaggeration of book quantities and the 'pro rata problem.'
'Bookman' shelf above by East Anglian artist Kazmierz Szmauz.