My personal opinion is that if a paladin is adventuring with a party who wants to sell Evil items rather than destroy them, he's probably adventuring with the wrong party.
My thoughts exactly. Ultimately, this is a PC interaction issue and should be resolved by PC in character interaction.
Destroying tools of evil is part of the job description. If the Paladin suddenly finds that he's questing in a party that objects to his goals, and in fact that he's not questing with a group of heroes, but rather adventuring with a bunch of sellsword mercenaries, then the Paladin would certainly end his association with the party. In fact, under some rules of Paladinhood, he
must end his association with the party, since the rules of Paladinhood traditionally forbid long term association with non-good characters. Failure to end such a relationship once the Paladin becomes aware of the issue is a breach of his code of conduct.
If I were RPing the Paladin in question, I'd probably first be somewhat taken a back, and perhaps assume niavely that the fighter cluelessly didn't realize that the sword was a work of daemonic evil, and would begin patiently explaining to the fighter what signs could be seen that indicated that the sword was a foul blasphamous object. Once the fighter clearly conveyed to the disbelieving Paladin the fact that he knew that the sword was evil, but that
he wanted to sell it for a profit to some other presumably evil being anyway, I think the Paladin would go through one hurt momment of 'You can't really mean that?', and then be forced to walk away and find a party that shared his goals of defeating evil.
As a short term solution, if the Paladin knew ahead of time that the party was just a group of greedy sellswords, a Paladin could legitimately agree that he will pay a fair price for (or get his supporting temple to pay) any evil artifact that comes into the party posession in order to take it off the market, but this is only a short term solution and one the party should have made clear. The Paladin can adventure under that sort of agreement only when he has no other choice and must find some allies to face the immediate threat or else allow evil to prosper. But he's not going to consider such a party to be his friends and comrades - merely some mercenaries he's been forced to hire.
In my campaigns, it just doesn't come up because the party knows that I'll be handing out XP story awards to all non-good players whenever objects of great evil are destroyed, and generally destroying the minor evil artifact that threatens the safety of the region is a story arc that comes up pretty regularly in my campaigns. Also my parties in long term campaigns tend to be very open to the idea that they are heroes and not merely mercenaries. The party rogue might wince ICly seing such valuable property destroyed, but he knows that a sermon is forthcoming if he actually voices those sentiments in front of the do-gooders in the party. They are also very much aware that if they sell an evil item of significant power on the open market, there is a very good chance that they will see it again in the hands of some other baddies. In fact, if they know me at all, they know that I'll go out of my way to make them have cause to regret such a rash act. This is a very strong incentive to destroy any item that has proved troublesome in the past.
As for the spellbook, if it didn't obviously radiate evil (and merely containing evil descriptor spells wouldn't cause it to do so IMO as a DM) and wasn't obviously written on human skin or something (as many of my necromatic tomes are), if I where the Paladin I'd almost certainly ask the party spellcaster for his expert opinion as to whether the book is evil. I'd do this less because I'm metagaming and wanting to ensure that the Wizard gets access to the spells, and more because it allows for some great RP oppurtunities. Besides which, I'm a Paladin, what do I know actually know IC about all this mysterious arcane magic?