Or it may not be an attempt to manipulate the market, just base on sources of information that price could go higher in the future.
Corner the market
- To buy most of a particular item or stock so that one can control its price.
The question is unclear. The phrase that may be sought is to "monopolize," to "hoard," or to "corner the market." Or it may be one or more of the virtually archaic words, "engross," "forestall," and "regrate" although those words tended to be restricted to activities in the market for basic foodstuffs or necessities. (See Wikipedia for a brief discussion of the three last verbs. A complete discussion of those terms would probably require a technical research article because those words are so little used nowadays, but Wikipedia is a convenient place to get a start on doing serious research.)
The primary reason for being so fuzzy about an answer is that the situation described requires very peculiar conditions to obtain (such as the market containing numerous "short sellers" who can, in the language of the stock market, be "squeezed.") That is why I mentioned the archaic words because those conditions either were common in medieval times or, more likely in my opinion, were mistakenly believed at the time to be common. But the fact that the common law considered engrossing, forestalling, and regrating to be crimes proves that the governments of the time believed them common enough to require a legal remedy. Of course, those same governments also believed witchcraft to be a crime common enough to require rather drastic remedies so the beliefs of 14th century governments do not strike me as invariably well founded, but that is personal opinion.
Without a great deal more specification on what the original question contemplates, any specific word may be wrong. Under NORMAL circumstances, the act of cornering the market will drive up prices, the resulting scarcity in the market will maintain high prices until new supplies become available, but the very act of selling to make a profit will alleviate the artificially induced shortage and thereby reduce prices to more normal levels and eliminate the profit.
This is called speculating. ODO's definition:
Invest in stocks, property, or other ventures in the hope of gain but with the risk of loss.
‘he didn't look as though he had the money to speculate in shares’
Wikipedia expounds a bit:
Speculation is the purchase of an asset (a commodity, goods, or real estate) with the hope that it will become more valuable at a future date.
So whether these are financial instruments or actual goods, it can still be called speculation.