It depends on how thinly traded the stock is. Unless it's very thinly traded or you trade it after hours you'll almost certainly be completely fine. Like if you're talking about something heavily traded like a FAANG, you could probably dump several thousand shares pretty much any time during regular trading hours and have little or no effect on the price. Certainly not enough to be worth caring about for a one time transaction. OTOH if you're running some trading algo that does that kind of transaction thousands of times a day (or more) every day, then that would be a very different story.