In my opinion, houses are usually bought because someone genuinely likes the property or thinks they can sell it for more, either way it is their choice, and is what make the game fun (you taking risks and choices). Hardly anyone gets manipulated to buying something they don’t want, and putting limits won’t do much if anybody is worried about manipulation. People will regret purchasing something (whether they lose 50k in the purchase or 500k, or 1M), but that’s normal.
That said, economy is changing, and in the case where someone really wants a house they will rather overpay than hear not selling, so I think there should be no limit at all.