Thais are generous people for the most part and in the past perhaps it would have been fine to take such an offer but not any more. In any country there are always those that prey on unsuspecting people. Car rentals Jeeps are readily available for hire by the day or week. Note that insurance coverage is not available for motorcycles. This also applies to your own injuries.
Larger vehicles take precedence over smaller ones at all times.
Please take care if you are planning on renting any kind of vehicle while visiting Phuket, especially a motorcycle. Thai driving is erratic at best and very dangerous at worst. Regular ferry services run between Phuket and Koh Phi Phi, the spectacular island group a couple of hours away to the east. Tour boats also do daytrips to the Similan Islands, about 50 miles to the north-west, which are famed for the quality of their diving. A lovely way to visit the nearby islands such as Coral Island or Koh Bon is to take a longtail boat.