Hi there Bugwink,
How are you doing? If diving in Guanacaste, the best option is to go further op north of Samara, around the area of Playas del Coco or Playa Hermosa. Here it is possible to do some beautifull dives just off shore.
As Chris already mentioned, shore dives are not that popular in Costa Rica.
Check out Rich Coast Diving, located in both Playas del Coco and Hermosa, they organise daily boattrips, every morning, and you'll always be back around 1 pm. Dive groups from the boat don't include more than 4 divers and you'll have a great change to see white-tip sharks, many different kinds of rays, turtles, but also beautifull small things like nudibranches and seahorses. You won't be dissapointed. If you get enthousiastic and like to go out a little bit further, you should deffinitely consider the Catalina Islands, an hour by boat, but there's a good change to meet the Manta Ray this time of year.
Rich coast diving can also help you finding accomodation, with or without divepackages.
If you have any further questions, please don't hesitate to contact me. Best Regards