In previous articles, I mentioned that when I go to local Chinese supermarkets, everyone - employees and customers - speaks to me in Chinese. With store employees, it is not that bad because the type of conversation is limited. I can get by with my limited Chinese and smiles! However, you are in a totally different playing field when other customers start talking to you! (I don't dare start a conversation with others!)
Sometimes, other customers look at my shopping cart and ask where I got the stuff. I usually understand the question if they ask in the simplest form (「〇〇在哪里？」(Where is ____?)). In that case, I usually answer in English, instead of saying “Sorry, I don't understand Chinese." (My Chinese is not good enought to explain locations of items. 
) Many usually just say, thank you or 谢谢 (thank you in Chinese) and walk away. But some, they start talking to me more in Chinese! WAIT! Yes, I understood your question in Chinese, but didn't you just observe that I can't speak it? I guess some people just don't care! I think some are so used to people who understand what they say but can't speak so me answering back in English is so normal to them. Some are just so eager to talk that I sometimes have to cut them off and say, "Sorry, I don't understand Chinese well." After that, some finally give up and walk away. And of course, there are some that will continue to talk to me in English.
The other day ...
I was buying something that my husband asked for. Since I was not familiar with the item, I took a picture of it with my phone before I headed to the store. At the store, I was looking at my phone (picture) trying to find what I was looking for. Then all of a sudden, some lady said something to me in Chinese so I told her I don't understand Chinese. Then she asked what I was looking for in English so I showed her my phone. She actually found the item for me! I thanked her for her help... then... She started to explain about the item that I was about to buy. AIYA!!! I was actually in hurry so I just said, "Sorry, I gotta go. My husband knows what it is so I am okay. Once again, thank you!" and left. I probably appeared bit rude but I knew this lady won't let me go so I did what I needed to do.
Do you talk with other customers in a store? I usually don't start a conversation, but if someone approaches me, I answer them in friendly manner. My friends won't believe this but I am actually not that outgoing, especially in unknown territories.