I bought these verbenas thinking they don't need deadheading but there is something wrong with them and I don't understand if they need to be cleaned from the dead flowers or if there is something else they are suffering from. They are watered every day and get full sun
Verbenas do need deadheading really, particularly the annual kinds such as yours - they look a lot tidier if they are deadheaded, removing the long stems with the spent flowers on the end, and this will encourage the plant to produce more flowers. Info here https://www.thespruce.com/verbena-care-1315718. If they aren't blooming very well after deadheading, or still look a bit tatty, clip them back by up to a third to encourage new growth.