He found an item being sold for a cheap price, and thinks that it is stolen goods; can he buy it?
Question

I found someone who had a wheelchair for rent or purchase in the street next to the Haram in Makkah, and I bought the wheelchair from him for approximately 200 riyals. There was a policeman nearby, and when I asked him about the price of wheelchairs in the shops, I found out that they are sold for no less than approximately 600 riyals. And I used the wheelchair. Please note that there was no writing on the wheelchair to indicate that it was for charity. I hope that you can advise me as to whether that was a valid transaction, especially since my mother used it when doing the rituals of ‘umrah.
Praise be to Allah.The cheapness of an item does not necessarily indicate that it is stolen goods. It may be fake, or the owner may be rich and no longer needs it, and he does not want to keep it as he no longer has any use for it, so he sells it cheaply, or he asks for a price lower than its real value because he wants to benefit visitors to the House of Allah, or there may be other reasons.
If the individual knows that the item is stolen, it is not permissible for him to buy it, because that comes under the heading of consuming people’s wealth unlawfully, and is also cooperating in sin and transgression. Allah, may He be exalted, says (interpretation of the meaning):
{And cooperate in righteousness and piety, but do not cooperate in sin and transgression. And fear Allah; indeed, Allah is severe in penalty} [al-Ma’idah 5:2].
Shaykh Ibn Baz (may Allah have mercy on him) was asked about buying stolen goods, and he replied:
What appears to be the case, based on shar‘i evidence, is that it is not permissible for you to buy it, if it is clear to you or you think it most likely that it was stolen, because Allah, may He be glorified, says (interpretation of the meaning): {but do not cooperate in sin and transgression} [al-Ma’idah 5:2].
And because you know or think it most likely that the seller is not the rightful owner of the item, and it is not permitted, according to Islamic teachings, to sell it. So how can you help him in his wrongdoing, and take the property of someone else unlawfully?"(Fatawa Ibn Baz  19/92).
Shaykh al-Albani was asked:
Is it permissible to buy an item that was possibly stolen for a price that is cheaper than the usual price?
Shaykh: The possibility of its having been stolen may vary, and rulings cannot be based on speculation and delusion. If the possibility is based on what is most likely to be the case, then it is not permissible to buy this item. Most shar‘i rulings are based on what the accountable person thinks is most likely to be the case. As for a mere passing thought, it is not permissible to go along with that thought and accept it, for that will lead to intrusive thoughts and illusions. End quote.
But if there is no sound likelihood of that, then the individual is not obliged to check and try to find out who the real owner of what is being offered for sale is. The basic principle is that items that being offered for sale belong to the one in whose hands they are.
And Allah knows best.