Alterations Question

Agreed with this. The pins will mark where the seams go and it shouldn't be any tighter than that. The pins also don't have as much structure as a seam does, so its actually pretty difficult to pin a dress too tight, so as long as the seamstress follows the pin markings (which they will), it should be fine. I wouldn't worry about it too much!

Did you sit down and move around in the dress when pinned? I had a fit and flare dress and would DEFINITELY recommend you do a squat or sit down in the dress before the seams are altered, as your standing hip circumference will likely be a bit smaller than your sitting hip circumference (and the widest part of your hips will be a bit lower on the dress when you sit, particularly if you have a bigger booty). My dress (which had no stretch) was perfectly fitted through the hips and thighs when standing but pretty challenging to sit in unless I was very careful. Note: I bought the dress pre-owned and gained a few pounds between my Covid elopement and wedding celebration a year later, so that fit issue was not a result of a poor tailoring but rather my body changing and the dress not specifically being tailored to my exact measurements at the time it was worn. This will also be less of an issue if your dress has a little stretch.

Whether or not a dress can be let out once it is taken it depends on how the seamstress/tailor does the seams. They will either keep the original fabric, resulting in more seam allowance and allowing the dress to be let out again, or trim the fabric to the appropriate seam allowance (5/8" or 1.5cm is considered standard). Keeping the excess fabric can result in a bulky seam that doesn't sit smoothly (particularly if there are bulky embellishments like beading), so chances are your seamstress will trim the fabric for your alterations, particularly if she is taking in more than an inch or so. If the amount the dress is being taken in is very minimal, he/she may leave the original hem.

I would discuss with your tailor/seamstress if you have concerns.