First of all I need to explain the difference between laminate and veneer. Many people use the terms interchangeably, but they are not the same thing. Veneer is a thin layer of wood covering a cheaper product. It can be sanded, painted and stained just like any other wood, but older pieces are often chipped or peeling. Those usually require a bit of gluing and wood putty. Laminate is like veneer in that it is a thin covering over a cheaper product, but it is not wood. It is man-made, often plastic. You CAN sand and paint it, but a primer is essential. It cannot be stained.
My cupboards were laminate. The insides were in great shape, but the outsides…not so much…well, at least the longer cupboard with the sliding front doors. I started by cleaning them up and giving them a light sanding, then they each got two good coats of primer. After these coats dried I gave the cupboards another thorough going over. Flaws that aren’t visible before often show more clearly after being primed. Glue and caulk are wonderful for correcting flaws on laminate furniture, but the base on the long cupboard was beyond fixable. Everything I did just seemed to make it crumble more. I finally gave up and removed it and built a new wood base.