How does a beneficiary know that the will is distributed properly?

If the estate was probated in court the estate becomes a public record. You can review the file. You may read the will, review the inventory for all the real and personal property listed and the value of the property, and then review any statements regarding distribution. You can also review the final account once it has been filed. If you have any questions, you can direct them to the executor and/or the attorney who is handling the estate.