I work with many first-time models and often do boudoir.
On the checklist I give them it says DON'T do this, but sometimes there will be someone who shows up to the shoot wearing a tight push-up bra.
Of course, this means any nudes or other photos we do without the push-up will have heavy marks on their body. These are a pain to edit in post.
How do I fix this DURING production?
Tell them to come back at the next available appointment time when they have followed the instructions you gave them.
Seriously. The only way to deal with this during production is to ensure it is dealt with prior to production. Make sure the client/model acknowledges at least a day in advance that they understand the need to wear loose fitting, non-binding clothing and underwear for several hours prior to the shoot so as to avoid compression marks on their body. To the best of my knowledge there is no quick fix way to make those marks go away any faster than they naturally do. Some body types will recover faster than others based on the relative amounts of fat or muscle tissue directly under the skin, but all of them still require time for the marks to go away.
If you have made this clear to them in advance, they have positively acknowledged the instructions, but yet show up anyway with binding underwear on it might mean they are consciously or otherwise communicating to you that they are not comfortable posing without these undergarments and hope that showing up for the session with underwear on that has created impressions on the skin means you won't ask them to remove that underwear during the session.
You can't get rid of compression marks easily. Rubbing or using moisturiser etc wont do anything, you just have to wait. So if they are there, you're stuck with fixing it in post and preparing better next time.
If you have a good makeup artist they can probably make them look all but gone, with a quick touch up in post.
Other than that, if you know you're doing a nude shoot make sure they are aware before the day. I know you give them a sheet, but most people probably skim read it. Perhaps a phone call or email a day or 2 before hand just to run through what you're doing etc and explicitly mention it then.
