This is a well known, and very crucial, issue for the planning of UBI. In the US, which retains an entrenched cultural contempt for the poor, exploitation by the market in poor neighborhoods has been a chronic problem. It was long common practice for the stores in poorer neighborhoods to raise prices at the same time of the month that welfare checks were distributed. And since banks would commonly refuse basic service to people below certain income levels, check cashing stores became common in poor neighborhoods, charging people to use their welfare money. In most every way, the poor pay more. This is why state governments began issuing EBT cards disguised to look like normal credit cards as an alternative to checks, staggering welfare disbursement across different times of the month so unscrupulous shopkeepers couldn’t exploit their poor customers and they wouldn’t need unscrupulous banks and check cashing stores to access their money.
Many fear this same kind of exploitation with UBI unless similar or other methods are used to curb this behavior by somehow making disbursement difficult to predict. When, in the mid 20th century, Louis Kelso proposed a system of UBI in the form of the Capital Homesteading Act the strategy was to base UBI on the annual dividend of a national mutual fund that every citizen had a individual account in and could choose to save or spend from as they wished. Merchants and landlords might know when dividends were disbursed, but month-to-month they would have no idea what people had in their individual accounts as the collective dividends would vary with the national productivity and people could save, spend, or roll-back into more fund shares whatever they wished.
In the Georgist context, a Land Value Tax is said to prevent landlords from passing taxes on to renters because the amount of property is fixed and the taxable value of the property is keyed to the rental value --ground rents. The more they charge in rent, the more they increase their property value and the more they are taxed on that value. Georgism is concerned with the capture of economic rents, that is unearned profits on the intrinsic value of exclusivity of a natural or socially-created resource rather than production. Use of a LVT encourages equilibrium and economic efficiency in real estate. It discourages the speculative holding of unused land, because that land will continue to be taxed whether or not the holder is making money from it, resists gentrification by discouraging property value inflation through cyclic recapitalization, and drives rents down by keying taxation to rent income. So even if landlords know they can extract a certain minimum amount of money from renters because of a UBI, the more they try to exploit that by inflating rents the more they’re taxed because they’ve inflated their property values.