If you wish to buy an item, you must declare interest in the thread. If there are multiple items on offer, you must specify which item(s) or how many you're interested in. In both cases, this should be clear and unambiguous. Please avoid vague statements like "PM sent"
or "I might be interested in...", use direct wording such as , "I am interested in...". The clearer you are in your assertions the less likely there will be any ambiguity as to who is next in line. Remember, English isn't everyone's first language here