One strategy Mormon apologists use is to excuse Joseph Smith's antics by claiming that his use of folk magic can be paralleled in the Bible. Let's consider that.
i) False prophets
We mustn't make a religious belief-system so flexible that it's impossible to show that someone is a false prophet. It is not in the self-interest of Mormons to stake their salvation on a charlatan. So they should want to have criteria that distinguish charlatans from true prophets. Certainly that's a running concern in the Bible, from the OT to the NT.
ii) Descriptive and prescriptive
The Bible describes examples of folk magic, viz., mandrakes as aphrodisiacs (Gen 30:14-17), sympathetic magic in selective breeding (Gen 30:37-42), teraphim (Gen 31:19,34; 1 Sam 19:13), a divination cup (Gen 44:2,5).
There is, though, a fundamental distinction between what the Bible describes and what the Bible prescribes. The fact that Scripture records a character doing something doesn't ipso facto carry any presumption of approval. Indeed, Scripture frequently records characters doing things which are prohibited and condemned.
Syncretism posed a chronic threat to OT Judaism. The law and the prophets condemn syncretism on a regular basis. Ancient Israelites were surrounded by heathen, superstitious cultures. It took constant vigilance to guard against moral and theological contamination.
The fact, for instance, that Gideon had a gimmick to determine God's will (Judges 6:36-40) doesn't imply divine approval rather than divine accommodation. That's very different from God proposing a sign (e.g. 2 Kgs 20:8-11).
iii) Randomizing device
Casting lots isn't necessarily a method to determine God's will. In some cases, it can simply be a randomizing device, in the same way we use coin flips to make impartial selections (e.g. Lev 16:7-10; 1 Chron 24:5,31; 25:8-9; 26:12-14; Lk 1:8-9). That's a fair way to make arbitrary selections. It eliminates favoritism.
To combine prayer with casting lots doesn't, by itself, indicate that casting lots is a way to determine God's will (e.g. Acts 1:23-26). For instance, Christians are often confronted with forced options. We must choose between alternate courses of action. We have a deadline. We pray about it, but making a decision isn't contingent on God answering our prayer. We can't compel God to give us guidance. We're not at liberty to refrain from action or wait to take action unless and until we have a sign or hear an audible voice. Circumstances force us to make a choice. If it's an arbitrary choice, we might use a randomizing device, like tossing a coin. Heads represent one course of action, tails another course of action. We hope and pray that God will bless our conscientious choice, but there's no presumption that God is bound to act on cue.
The OT discourages a talismanic mentality. Saul found out the hard way that God's will could not be mechanically compelled (1 Sam 28:6). Likewise, when the Israelites superstitiously treated the ark of the covenant as a rabbit's foot, their plan backfired (1 Sam 4). God humiliated their presumption.
iv) Authorized/unauthorized divination
There's a fundamental distinction between licit and illicit divination. The Urim and Thummin was a form of divinely sanctioned divination. We don't know what it was or how it worked. But it could sometimes be used to determine God's will. That, however, doesn't license the use of divination in general, which is condemned in the Mosaic law.
Another example is trial by water ordeal (Num 5). That's a miraculous maternity test. But that doesn't mean people are entitled to concoct their own gimmicks.
v) Bronze snake
Num 21 appears to be an example of polemical theology. It appropriates popular belief in sympathetic magic, but uses that ironically to subvert paganism, like burning an effigy:
It is clear that the uraeus was a fiery snake which the Egyptians believed would protect the Pharaoh by spitting forth fire on his enemies…Clearly, then, the biblical writer employed Egyptian background material and motifs when recording the Num 21 incident…The raising up of the bronze serpent on a standard may also be a symbol of Yahweh's vanquishing Egypt. The Egyptians fashioned images of threatening forces in order to demolish those forces…Sometimes it is the hostile power to be destroyed that is thus counterfeited and done to death. So the replication of snakes, scorpions, crocodiles, and the like not only served to protect whoever made use of such an image, but on occasion functioned as a force of destruction against the object represented. Since the serpent was the emblem of ancient Egyptian sacral and regal sovereignty, Yahweh's command in Num 21 to fashion a model of a serpent was a sign of his conquering the nation. This point would be especially clear to those Hebrews who desired to return to Egypt and who believed that their security and deliverance rested in Pharaoh and his people. Yahweh was proclaiming the annihilation of Egypt. Egypt could in no way liberate Israel. Salvation came only from the hand of Yahweh. J. Currid, Ancient Egypt and the Old Testament (Baker, 2001), 147-49.