Yes, in most cases there's at least some room to negotiate, particularly for longer leases, units that have been listed for a while, or during the quieter low season (roughly May to October). It's rarely a huge amount -- 5-10% off the asking price is a realistic range -- but it's usually worth a polite ask.
The safest way to raise it is to frame the request around commitment rather than simply asking for a discount: offering a 12-month lease instead of 6, or paying several months in advance, gives the landlord a reason to say yes rather than feeling pressured. It also helps to have a specific, comparable listing in mind if you're asking because a unit seems priced above similar ones nearby, since a concrete comparison lands better than a general "can you do better on the price."
Landlords in Jomtien are generally used to being asked, so a reasonable, respectful offer won't cause offence -- what tends not to land well is asking for a large reduction with no justification, or negotiating after verbally agreeing to a price. If you'd rather not negotiate directly yourself, we're happy to handle that conversation on your behalf when you view a unit through us.