As for post-maintenance, as long as you choose a relatively formal network company, you can ensure normal maintenance. If there are any changes or problems on the website, most of them can reply immediately by calling.
Having said that, I would like to add that when the website is built and handed over to you for testing, you must take the time to test it comprehensively and go through the functions of each page to avoid starting to react after handing in the work. Of course, it is difficult to see all the problems in a short time. For example, some loopholes that were not seen in the early stage, including some database information that requires a lot of data to find problems.
As long as the problems found in the use are in the development function negotiated by both parties, the network company should solve them. If the problems you find or the amendments you propose are beyond the scope of previous negotiations, there may be a request for an increase in fees. It depends on the friendly negotiation between you at this time.
If our "Han Bang Future" company meets such customers, they are generally friendly:)