No -- key money or "goodwill" payments (an extra upfront sum paid to secure a lease, on top of the deposit and advance rent) are not standard practice when renting a condo in Jomtien. This is common in some other rental markets, but it isn't part of how residential leasing works here.
What you should expect to pay upfront is the security deposit (typically one to two months' rent) and the first month's rent in advance. Beyond that, some agents charge a fee for arranging the rental, though this is usually disclosed clearly upfront and is separate from anything paid to the landlord.
If anyone asks for an additional unexplained upfront payment beyond deposit, advance rent and a clearly stated agent fee, it's worth asking exactly what it's for before paying. It's not necessarily a red flag on its own, but it's not standard, so get a clear explanation and, ideally, something in writing.