Concerns and red flags

Although it is more common in other types of lizards, mouth rot is a concern. This usually occurs when the gecko bangs or smashes his snout on something. Geckos strike when they eat much like a snake and often miss and hit rocks and other things. Mouth rot is a pretty gross looking yellowish puss on the snout or mouth. If you catch this early you can treat it easily by cleaning the wound with peroxide and applying Vaseline to help it heal...it should clear up in a day or two.
Skin infections will appear as brown or black spots on the feet or underbelly of the gecko. Typically caused by soiled substrate, this is also easily dealt with. Just clean the tank throughly and swap the spots with Neosporin.
Bugs such as ticks and mites are rarely a problem and rarely fatal. However they can make Mr. Gecko really uncomfortable. Do not use insect strips!! They could poison your gecko. A pet store will have a reptile safe pyrethrin spray that works great.
Calcium deficiency is pretty common among gecko species. Their bodies require calcium to digest food. Indications include soft jaws and distorted limbs. This can be corrected (and prevented) by providing plenty of vitamins and supplements for your gecko and crickets.

I don’t want to dwell on this section too long as most of these problems are unlikely as long as your gecko is well cared for. Don’t let this scare you away from becoming a gecko owner.