When do you need a surveyor ?

[Radiowaves]

Many large dealers like Surfside 3 here in NY sell pre-owned boats that were traded in, usually during a trade up. Most are 1-5 years old and will come with a warrantee. At what point must you do a survey or is it just advised because most dealers will stand behind the sale. I know if there will be a loan from a bank you most likely will need to have the boat surveyed. Do dealers do this for you?