If she answers "Let me check with my BF" you have a pretty good idea. lol

Truth be told, there really is no way to know. Sometimes providers will "invent" a BF where there is not one to keep her clingier clients at arms length. Other times a provider will pretend her BF doesn't exist to keep the GFE fantasy alive.

In short, there really is no way to know for sure, I suppose the best answer to your question is to buy gifts that only she would get any use out of.

Lastly, don't buy cheap wine, I hate it when my GF ends up with a dozen bottles of undrinkable wine stacked up that neither of us will drink. lol

just ask her? I can't really think of any gifts you may give that he would want even if she did have a boyfriend. Ask for a wishlist.

By boyfriend I mean pimp. By gift I mean the donation.

I actually agree with GaGa.  I ran into a BF problem once.   I went to see this lady once.  Arrived.  Texted.   Waited 30 minutes.  Got the green light.  Went up.  Long story short, her BF and her just had an argument.   He wanted her to stop doing this.  After the session, she told me that he was in the parking lot in his car.  Talk about weird.   I didn't see anyone for months afterwards because I was freaked out.

... and you shake hands and make small talk.  Maybe avoid talking about how she just blew your mind... and other things.  

I've met my ATF's SO several times. Cool guy.  I haven't met the boyfriends/girlfriends/SOs for any other providers but some have mentioned to me they're in a relationship.  It's none of my business. I never ask providers about it, but some volunteer it.  

Funny you mentioned that you want to make sure the gift you give a provider is hers. I used to give my ATF gift certificates for our fav massage therapist, until I found out from said therapist that my ATF hadn't been in for a long time... but her SO comes in a lot. I asked my ATF about it and she said she doesn't have time for massages and besides gets them from some of her clients (like me), so she gave the certificates to her SO. So no more massage certificates for her!

I had zero desire to meet the guy.  She did openly discuss their relationship, something that was a bit of a turn off.  She was an independent and was not working for an agency.  Her boyfriend served in the Marines.  I am also retired military, but I didn't do the full 20 years.  She receives government benefits while she flies under the radar.  She is actually in the TER 100 for DC.  I am not going to provide any more details.