The Big Customer quest in Escape From Tarkov is available to complete on the Customs map, the second location added to the game. It is given to you by Pavel Yegorovich Romanenko, known by his alias "Prapor". Note that this quest needs some special requirements. Big Customer is activated after accepting Chemical - Part 4. By completing either Chemical - Part 4 or Out of Curiosity, you will auto-fail and lose access to this quest. Here is all you need to know to complete Documents in Escape from Tarkov.
Steps in completing Big Customer in Escape From Tarkov
Locate the transport with the chemicals on Customs
Mark the vehicle with an MS2000 Marker
Survive and extract from the location
You’ll need to buy the MS2000 Marker from Prapor or Ragman. Click on the ‘S’ icon on the tabs and you’ll find the marker. You only need to buy one marker to complete this quest.
Head towards the north of the ZB-1012 extract point, next to Warehouse 4 on the Customs map to complete the quest.
Beware of the sniper scav that is stationed on the roof of the warehouse building you need to enter.
Look for the van with a pole sticking out from the engine.
Head to the back of the van and place the MS2000 marker there. You must stay alive for 30 seconds after you place the marker to complete the objective. You can choose to complete the quest with either the Therapist, Skier or Prapor.
Once you complete all the objectives, it is important to note that players must extract safely without being killed by enemy players or Scavs. Completing the Big Customer quest with Skier will get you the option to buy the ZSh-1-2M helmet from Ragman at level 3. If you complete the quest with the Therapist you will get a Medicine case and 170,000 Roubles.
Prapor will get you the following rewards:
+8,100 EXP
Prapor Rep +0.03
200,000 Roubles
210,000 Roubles with Intelligence Center Level 1
230,000 Roubles with Intelligence Center Level 2
1× 6B2 body armor (Flora)
2× Ammunition case