ahirsch

For sampling, I always ask, unless the supermarket has like toothpicks and garbage cans specifically for sampling (like with olives).

Regarding eating for food before paying for it, I think it depends on cultural considerations. In many places snacking while shopping is very common. In other places, it is frowned upon. If it needs to be weighed, I would only eat it if the products already have a price sticker (like in the baked goods section). Otherwise, you are paying for less than what you bought.

Easiest solution is to ask someone in the store if they mind.

I would say a blech is much more dangerous than a hot plate, since it is a gas fire all night.

But regarding electric hot plates, it depends who you ask. Worst case scenario, a hot plate should be treated like a blech, which means that you can’t put something cold directly on the surface. You use like an inverted pan or something like that. This is because of the issue of “michzei kemevashe” or looks like you are cooking.

Harav Elyashiv said that a hot plate should be treated like a blech in all aspects. Harav Ovadia Yosef and others have said that a hot plate is not used for cooking, so it doesn’t have the problem of michzei kemevashel and so you can put food (dry of course) directly on the hot plate. Harav Shlomo Zalman Aurbach writes that it makes sense to be more lenient with a hot plate like Harav Ovadia, but it is better to be machmir. Harav Dov Lior (chief rabbi of Kiryat Arba and Chevron) holds like Harav Ovadia.