At the time of closing the keys to the home should have been made available to the buyer or to the buyer's agent. Any mortgage that the seller had on the property will have been paid off by the title company, as will any outstanding HOA dues or property taxes.
All future bills for HOA fees and property taxes should be directed to the buyer. The HOA will have been informed that the property has changed hands by the title company as part of their check that no fees are outstanding. The county tax office should also pick up on the sale when the deed to the property is recorded.
Occasionally these things to not happen exactly as they should. If the seller receives a bill for something that is now the responsibility of the new owner, or vice versa, it is important that the vendor should be made aware of the change of ownership promptly.
If the buyer is taking over advance rental bookings from the previous owner he has the responsibility of making immediate contact with each renter to explain what is happening, and of making sure that each rental, including any that are in place at the date of closing, is managed professionally.
The buyer will receive a packge of documents after closing, including the title insurance policy. The other particularly important piece of paper, the recorded title deed, will be mailed a few weeks later, as it takes some time for the deed to be recorded by the county or city as appropriate and then copied back to the title company.
If either the seller or the buyer has any concerns that there may be an unresolved issue after closing they should initially ask their real estate agent to look into it. He or she in turn will communicate with the title company or any other agency as necessary.