Let's start with the beneficiaries. My general observation is that beneficiaries need to temper their expectations. Before you demand information from an executor, be sure that you are a person who is entitled to the information. If you are not a residuary beneficiary, then the executor does not have to tell you how much the house was sold for, or who got Mom's bedroom suite. It's simply none of your business, even if that doesn't seem fair to you.
Beneficiaries also need to be reasonable about what they ask for. For example, not everyone can demand to have the originals of everything, since there is only one original. When you ask an executor for an accounting, be specific. For example, you could ask what was paid to realtors and lawyers in the house sale. You are much more likely to hear the answer you want if you ask the right question. Sometimes beneficiaries will complain that they weren't told how much was in Dad's bank account, and when I ask whether they enquired about the bank account, they say they didn't. So, rather than talking to me, they should be directing a specific question to the executor.
Also, be reasonable in the time you allow for a response. Most executors are also juggling jobs, homes, and families along with their executor work and may not be able to drop everything to respond to your question. Set a reasonable deadline, such as a week, for a reply.
Now, on to the executors. I often wonder why so many executors are so unwilling to give information to beneficiaries. It isn't in your best interests to ignore requests, or worse, to respond with hostility. If you refuse to cooperate with reasonable requests for information, the beneficiary has the option to take you to court to force you to respond. This doesn't usually end well for executors, simply because judges get a bit sick of playing referee for grown people who should be able to manage these things between themselves. Sometimes the executor is punished by the judge by way of being ordered to forego the executor fee, or being removed from the estate entirely.
Executors, you are required to share all financial information with the residuary beneficiaries of the estate. Maybe you don't want to, and maybe you think those people are being a pain in the neck with all their questions, but that's the job. You agreed to be the executor and this is part of what you have to do.
This doesn't mean you have to jump every time someone barks at you. You have to give full, accurate answers in a reasonable time, but if someone is calling you at 2:00 am with a desperate need to know how much you sold Dad's car for, you are within your rights to tell that person to go away.
The best advice I can give executors is to keep your records up to date, and as detailed as possible. Be transparent because I can guarantee that the more you keep information to yourself, the more the other people involved in the estate will suspect you of wrongdoing.
I'd like to remind both beneficiaries and executors that basic courtesy, respect, and manners go a long, long way to getting optimum results and minimizing conflict. I'd also like to remind them that most executors are family, and before heading off to court to beat answers out of each other, you might try mediation and talking to resolve your differences.