Once upon a time, a long long time ago, it was possible to identify and contact other members by looking through a user's feedback but then ebay made the identity of a seller's buyers anonymous to everyone except the buyer and seller in question.
This might be one of the reasons they did that.
While it is tempting to look for patterns of outcomes with transactions, the fairest thing to do is judge each situation on its own merit. I understand the reason you would like to reach out to your fellow buyers but it probably shouldn't be done even if it could be done. Just because something went awry with their orders (possibly) doesn't necessarily mean the same will happen to you and yours.
If it does, we are supposed to place our faith in ebay as a governing body to put a stop to it.
Mark your estimated delivery date on the calendar and follow-up with the seller if you don't have it by that time. A seller really cannot change the estimated delivery date after your order was placed, it is up to the seller to meet their stated handling time or face the consequences from ebay if they do not. Please note 'placed' means when you paid for it, not when it was bought. There may be a delay between the two which is of the buyer's own creation. If you waited a week to pay for something, you cannot expect your seller to compensate by shipping it to you at a faster service than you paid for.
If there is a weird glitch that led to incorrect delivery estimates being displayed on the listing and/or Order Details (that is the delivery estimate that counts) then ebay itself may be to blame for it and not the seller. (There may have recently been an update to the estimates for Economy on ebay.com but I'm not 100 per cent certain of that.)
If, on the other hand, the order details say it is due for delivery by Nov. 30 but your seller says in a message or email to you that you should expect it Dec.15, that is the seller's problem. You need to go by the Order Details. It is the seller's responsibility to have their listings established correctly so that the buyer gets the correct estimate, barring some technical failing on the part of the ebay system which does happen form time to time.
Maybe if you with back with more details about what has led you to worry (but without identifying the seller, please, as that is not allowed) we can give you more specific advice.
But...... when I look at the last seller to have left feedback for you and wonder if this is the seller you are asking about, I understand all too well your reason to be worried. Is this a dress that you need for a certain date? If so, I would start looking at a Plan B. Buying high-end dresses from overseas for special events is, to my way of thinking, risky. You need a contingency plan. Even if you never have to use it, you need to be prepared for a non-arrival and/or a dress that does not fit its description or you. Sorry to be the bearer of that news. I am a toy seller but maybe another clothing seller on ebay.ca can give you better advice than me.
