I can appreciate your caution but my feeling is that if you genuinely noticed it innocently because they left their garage door open and you were driving by then there is no harm in you knocking on their door and introducing yourself and saying that you are an arcade enthusiast and happened to notice the <insert game name> sitting in their garage and wanted to know more about it and if it might be for sale. Unfortunately we live n a society where some bad apples and a lot of negative media has put people on high alert for unscrupulous types. But if that is not you then I don't think it should prevent you from a friendly visit. If the owner can't seem to get past their guardedness and gives you the cold shoulder and ends you on your way then oh well. If someone were to do it to me, the way I react is going to have everything to do with my impression of them, what they say, how they act, how they look, the total package. I have a pond in my front yard that is shared by 2 neighbors on other sides. I came home once to 2 people fishing in my front yard. They saw me pull up and did nothing. I had to go out to them to see what was going on. They were polite enough when I talked to them and told me they were friends of one of my neighbors and hoped I didn't mind them fishing in my yard. I told them that if they had waited until I was home and knocked on my door to introduce themselves and asked if they could fish before just doing it that I probably wouldn't have minded. But since they just decided to do it anyway without asking that yes, I did mind and to please leave. They left without even an apology. A few days later I found some dead fish left on my dock. I guess they didn't like my answer. I haven't seen them since. If they had the balls to show up, knock on my door, and apologize for their initial intrusion I might see fit to forgive them but I guess they don't have the character to do that. My point is that if you are polite, courteous, and respectful, you should not feel bad about going up and asking a strange neighbor about a game you saw by chance.