Note that the boat fee (350 baht slow boat, 600 baht speedboat) includes transport to/from Trat. Some hotels will try to rip you off by requesting hundreds of baht for the transport to the pier. Do not agree to this, and if you find the deal changes when you arrive at the pier and the boat operators (who run the taxis as well) try to force you to pay this fee, and taxi drivers/boat operators are connected in a sort of Mafia-style operation. Feel free to politely mention that you may need to phone the tourist police and wait for a resolution if this happens to you. To be fair to the boat operators this hardly ever happens.
If you take the slow boat and book ahead, some resorts will pick you up from the pier. If you take the speed boat, you will usually be dropped at or very close to your destination so this is not required