If you buy online, the wisest choice is to be sure that the seller is reputable and knows something about sewing and patterns. We have all heard stories of how a buyer can be "surprised" when the pattern they purchased was not as described or in the condition they expted.
Communication is so important, try to find sellers who can answer questions and assist you in making the right choice. Often buying from a source that says they cannot answer questions and all sales are final often means that there might be issues with the pattern that a person who sews would notice and mention in their listing. Sometimes there is no problem with the pattern buy having a knowledgeable certainly is an advantage.
Vintage patterns are very popular now, but there are a few things to be aware of before you buy. For example, before about 1968, the sizing was different that our modern sizing. So if the measurements or size chart is not present in their listing for you to review be sure to ask for that information before you make your selection. When the modern sizing was introduced, you will often see a note on the pattern envelope that says something like “new sizing”.
Condition of vintage patterns can be key. Since pattern envelope and pattern tissue are often made of fragile paper, you will want to be sure that the condition of the item is up to your expectations and there are no missing pieces or any other situation that would make it not useable to you. Some older patterns, especially those produced during WWII can be plain tissue with just the piece letter or number perforated to identify it. These patterns are perfectly fine to use as you would printed patterns, but it is advisable that once you receive a plain tissue pattern, that you write the company name and pattern number (i.e. Simplicity 3823) on each piece before using so in the event the piece get misplaced you can rematch it to the right pattern.
In addition to sewing patterns, there are also patterns for crochet for example where you can crochet a swimsuit, cover-up and hat for the beach. So your creativity for your seasonal wardrobe is not limited just to sewing patterns. It is not often possible to find ‘mint condition’ sewing patterns that are 40, 50 or 60 years old.
I hope these tips will help you choose the best pattern for your warm weather enjoyment.